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-rw-r--r--.github/workflows/docker.yml2
-rw-r--r--.github/workflows/docs-pr-netlify.yaml2
-rw-r--r--Cargo.lock4
-rw-r--r--changelog.d/17172.feature2
-rw-r--r--changelog.d/17187.feature1
-rw-r--r--changelog.d/17254.bugfix1
-rw-r--r--changelog.d/17256.feature1
-rw-r--r--changelog.d/17265.misc1
-rw-r--r--changelog.d/17266.misc1
-rw-r--r--changelog.d/17270.feature1
-rw-r--r--changelog.d/17271.misc1
-rw-r--r--changelog.d/17272.bugfix1
-rw-r--r--changelog.d/17273.misc1
-rw-r--r--changelog.d/17275.bugfix1
-rw-r--r--changelog.d/17277.feature1
-rw-r--r--changelog.d/17279.misc1
-rw-r--r--changelog.d/17281.feature1
-rw-r--r--changelog.d/17282.feature1
-rw-r--r--changelog.d/17284.feature1
-rw-r--r--changelog.d/17293.feature1
-rw-r--r--changelog.d/17295.bugfix1
-rw-r--r--changelog.d/17296.feature1
-rw-r--r--changelog.d/17297.misc1
-rw-r--r--changelog.d/17300.misc1
-rw-r--r--changelog.d/17301.bugfix1
-rw-r--r--changelog.d/17308.doc1
-rw-r--r--changelog.d/17322.feature1
-rw-r--r--docker/complement/conf/workers-shared-extra.yaml.j22
-rw-r--r--docs/usage/configuration/config_documentation.md20
-rw-r--r--poetry.lock216
-rw-r--r--rust/src/events/internal_metadata.rs3
-rwxr-xr-xscripts-dev/complement.sh1
-rw-r--r--synapse/api/constants.py4
-rw-r--r--synapse/config/experimental.py13
-rw-r--r--synapse/config/ratelimiting.py10
-rw-r--r--synapse/events/utils.py2
-rw-r--r--synapse/events/validator.py2
-rw-r--r--synapse/federation/federation_client.py7
-rw-r--r--synapse/federation/federation_server.py4
-rw-r--r--synapse/federation/transport/client.py9
-rw-r--r--synapse/federation/transport/server/__init__.py24
-rw-r--r--synapse/federation/transport/server/_base.py24
-rw-r--r--synapse/federation/transport/server/federation.py41
-rw-r--r--synapse/handlers/admin.py12
-rw-r--r--synapse/handlers/e2e_keys.py108
-rw-r--r--synapse/handlers/e2e_room_keys.py18
-rw-r--r--synapse/handlers/events.py2
-rw-r--r--synapse/handlers/initial_sync.py5
-rw-r--r--synapse/handlers/message.py3
-rw-r--r--synapse/handlers/pagination.py3
-rw-r--r--synapse/handlers/relations.py3
-rw-r--r--synapse/handlers/room.py60
-rw-r--r--synapse/handlers/search.py4
-rw-r--r--synapse/handlers/sliding_sync.py667
-rw-r--r--synapse/handlers/sync.py132
-rw-r--r--synapse/http/matrixfederationclient.py55
-rw-r--r--synapse/media/_base.py63
-rw-r--r--synapse/media/media_repository.py61
-rw-r--r--synapse/media/media_storage.py223
-rw-r--r--synapse/media/storage_provider.py40
-rw-r--r--synapse/media/thumbnailer.py6
-rw-r--r--synapse/notifier.py1
-rw-r--r--synapse/push/mailer.py1
-rw-r--r--synapse/rest/__init__.py4
-rw-r--r--synapse/rest/admin/experimental_features.py1
-rw-r--r--synapse/rest/client/account.py6
-rw-r--r--synapse/rest/client/devices.py4
-rw-r--r--synapse/rest/client/directory.py2
-rw-r--r--synapse/rest/client/keys.py92
-rw-r--r--synapse/rest/client/knock.py8
-rw-r--r--synapse/rest/client/media.py2
-rw-r--r--synapse/rest/client/models.py99
-rw-r--r--synapse/rest/client/reporting.py (renamed from synapse/rest/client/report_event.py)65
-rw-r--r--synapse/rest/client/room.py11
-rw-r--r--synapse/rest/client/sync.py230
-rw-r--r--synapse/rest/client/versions.py2
-rw-r--r--synapse/rest/key/v2/remote_key_resource.py2
-rw-r--r--synapse/rest/media/download_resource.py8
-rw-r--r--synapse/rest/media/thumbnail_resource.py2
-rw-r--r--synapse/server.py4
-rw-r--r--synapse/storage/controllers/state.py87
-rw-r--r--synapse/storage/databases/main/events.py1
-rw-r--r--synapse/storage/databases/main/events_worker.py16
-rw-r--r--synapse/storage/databases/main/room.py32
-rw-r--r--synapse/storage/databases/main/roommember.py14
-rw-r--r--synapse/storage/databases/main/stream.py74
-rw-r--r--synapse/storage/databases/main/user_directory.py66
-rw-r--r--synapse/storage/roommember.py2
-rw-r--r--synapse/storage/schema/main/delta/85/06_add_room_reports.sql20
-rw-r--r--synapse/synapse_rust/events.pyi2
-rw-r--r--synapse/types/handlers/__init__.py252
-rw-r--r--synapse/types/rest/__init__.py (renamed from synapse/rest/models.py)0
-rw-r--r--synapse/types/rest/client/__init__.py309
-rw-r--r--synapse/visibility.py14
-rw-r--r--tests/events/test_utils.py3
-rw-r--r--tests/federation/test_federation_media.py234
-rw-r--r--tests/handlers/test_oauth_delegation.py2
-rw-r--r--tests/handlers/test_sliding_sync.py1476
-rw-r--r--tests/handlers/test_user_directory.py39
-rw-r--r--tests/media/test_media_storage.py239
-rw-r--r--tests/push/test_email.py37
-rw-r--r--tests/replication/storage/test_events.py13
-rw-r--r--tests/rest/admin/test_admin.py4
-rw-r--r--tests/rest/admin/test_event_reports.py6
-rw-r--r--tests/rest/client/test_account.py28
-rw-r--r--tests/rest/client/test_keys.py65
-rw-r--r--tests/rest/client/test_models.py2
-rw-r--r--tests/rest/client/test_reporting.py (renamed from tests/rest/client/test_report_event.py)93
-rw-r--r--tests/rest/client/test_retention.py1
-rw-r--r--tests/rest/client/test_sync.py314
-rw-r--r--tests/rest/client/utils.py5
-rw-r--r--tests/storage/test_event_chain.py1
-rw-r--r--tests/storage/test_stream.py279
-rw-r--r--tests/storage/test_user_directory.py4
-rw-r--r--tests/test_visibility.py10
115 files changed, 5460 insertions, 708 deletions
diff --git a/.github/workflows/docker.yml b/.github/workflows/docker.yml
index 391e9c96ff..06aaeb851f 100644
--- a/.github/workflows/docker.yml
+++ b/.github/workflows/docker.yml
@@ -72,7 +72,7 @@ jobs:
 
       - name: Build and push all platforms
         id: build-and-push
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           push: true
           labels: |
diff --git a/.github/workflows/docs-pr-netlify.yaml b/.github/workflows/docs-pr-netlify.yaml
index 277083ded3..6d184a21e0 100644
--- a/.github/workflows/docs-pr-netlify.yaml
+++ b/.github/workflows/docs-pr-netlify.yaml
@@ -14,7 +14,7 @@ jobs:
       # There's a 'download artifact' action, but it hasn't been updated for the workflow_run action
       # (https://github.com/actions/download-artifact/issues/60) so instead we get this mess:
       - name: 📥 Download artifact
-        uses: dawidd6/action-download-artifact@09f2f74827fd3a8607589e5ad7f9398816f540fe # v3.1.4
+        uses: dawidd6/action-download-artifact@bf251b5aa9c2f7eeb574a96ee720e24f801b7c11 # v6
         with:
           workflow: docs-pr.yaml
           run_id: ${{ github.event.workflow_run.id }}
diff --git a/Cargo.lock b/Cargo.lock
index e3e63fc205..7472e16291 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -444,9 +444,9 @@ dependencies = [
 
 [[package]]
 name = "regex"
-version = "1.10.4"
+version = "1.10.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c117dbdfde9c8308975b6a18d71f3f385c89461f7b3fb054288ecf2a2058ba4c"
+checksum = "b91213439dad192326a0d7c6ee3955910425f441d7038e0d6933b0aec5c4517f"
 dependencies = [
  "aho-corasick",
  "memchr",
diff --git a/changelog.d/17172.feature b/changelog.d/17172.feature
new file mode 100644
index 0000000000..245dea815c
--- /dev/null
+++ b/changelog.d/17172.feature
@@ -0,0 +1,2 @@
+Support [MSC3916](https://github.com/matrix-org/matrix-spec-proposals/blob/rav/authentication-for-media/proposals/3916-authentication-for-media.md)
+by adding a federation /download endpoint (#17172).
\ No newline at end of file
diff --git a/changelog.d/17187.feature b/changelog.d/17187.feature
new file mode 100644
index 0000000000..50383cb4a4
--- /dev/null
+++ b/changelog.d/17187.feature
@@ -0,0 +1 @@
+Add initial implementation of an experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint.
diff --git a/changelog.d/17254.bugfix b/changelog.d/17254.bugfix
new file mode 100644
index 0000000000..b0d61309e2
--- /dev/null
+++ b/changelog.d/17254.bugfix
@@ -0,0 +1 @@
+Fix searching for users with their exact localpart whose ID includes a hyphen.
diff --git a/changelog.d/17256.feature b/changelog.d/17256.feature
new file mode 100644
index 0000000000..6ec4cb7a31
--- /dev/null
+++ b/changelog.d/17256.feature
@@ -0,0 +1 @@
+ Improve ratelimiting in Synapse (#17256).
\ No newline at end of file
diff --git a/changelog.d/17265.misc b/changelog.d/17265.misc
new file mode 100644
index 0000000000..e6d4d8b4ee
--- /dev/null
+++ b/changelog.d/17265.misc
@@ -0,0 +1 @@
+Use fully-qualified `PersistedEventPosition` when returning `RoomsForUser` to facilitate proper comparisons and `RoomStreamToken` generation.
diff --git a/changelog.d/17266.misc b/changelog.d/17266.misc
new file mode 100644
index 0000000000..ce8c4ab086
--- /dev/null
+++ b/changelog.d/17266.misc
@@ -0,0 +1 @@
+Add debug logging for when room keys are uploaded, including whether they are replacing other room keys.
\ No newline at end of file
diff --git a/changelog.d/17270.feature b/changelog.d/17270.feature
new file mode 100644
index 0000000000..4ea5e7be85
--- /dev/null
+++ b/changelog.d/17270.feature
@@ -0,0 +1 @@
+Add support for the unstable [MSC4151](https://github.com/matrix-org/matrix-spec-proposals/pull/4151) report room API.
diff --git a/changelog.d/17271.misc b/changelog.d/17271.misc
new file mode 100644
index 0000000000..915d717ad7
--- /dev/null
+++ b/changelog.d/17271.misc
@@ -0,0 +1 @@
+Handle OTK uploads off master.
diff --git a/changelog.d/17272.bugfix b/changelog.d/17272.bugfix
new file mode 100644
index 0000000000..83e7ca426a
--- /dev/null
+++ b/changelog.d/17272.bugfix
@@ -0,0 +1 @@
+Fix wrong retention policy being used when filtering events.
diff --git a/changelog.d/17273.misc b/changelog.d/17273.misc
new file mode 100644
index 0000000000..2c1c6bc0d5
--- /dev/null
+++ b/changelog.d/17273.misc
@@ -0,0 +1 @@
+Don't try and resync devices for remote users whose servers are marked as down.
diff --git a/changelog.d/17275.bugfix b/changelog.d/17275.bugfix
new file mode 100644
index 0000000000..eb522bb997
--- /dev/null
+++ b/changelog.d/17275.bugfix
@@ -0,0 +1 @@
+Fix bug where OTKs were not always included in `/sync` response when using workers.
diff --git a/changelog.d/17277.feature b/changelog.d/17277.feature
new file mode 100644
index 0000000000..5c16342c11
--- /dev/null
+++ b/changelog.d/17277.feature
@@ -0,0 +1 @@
+Add `is_dm` filtering to experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint.
diff --git a/changelog.d/17279.misc b/changelog.d/17279.misc
new file mode 100644
index 0000000000..2090b11d7f
--- /dev/null
+++ b/changelog.d/17279.misc
@@ -0,0 +1 @@
+Re-organize Pydantic models and types used in handlers.
diff --git a/changelog.d/17281.feature b/changelog.d/17281.feature
new file mode 100644
index 0000000000..fce512692c
--- /dev/null
+++ b/changelog.d/17281.feature
@@ -0,0 +1 @@
+Add `is_encrypted` filtering to experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint.
diff --git a/changelog.d/17282.feature b/changelog.d/17282.feature
new file mode 100644
index 0000000000..334709a3a7
--- /dev/null
+++ b/changelog.d/17282.feature
@@ -0,0 +1 @@
+Include user membership in events served to clients, per MSC4115.
\ No newline at end of file
diff --git a/changelog.d/17284.feature b/changelog.d/17284.feature
new file mode 100644
index 0000000000..015d925e7c
--- /dev/null
+++ b/changelog.d/17284.feature
@@ -0,0 +1 @@
+Do not require user-interactive authentication for uploading cross-signing keys for the first time, per MSC3967.
\ No newline at end of file
diff --git a/changelog.d/17293.feature b/changelog.d/17293.feature
new file mode 100644
index 0000000000..60ca7721a0
--- /dev/null
+++ b/changelog.d/17293.feature
@@ -0,0 +1 @@
+Add `stream_ordering` sort to experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint.
diff --git a/changelog.d/17295.bugfix b/changelog.d/17295.bugfix
new file mode 100644
index 0000000000..4484253bb8
--- /dev/null
+++ b/changelog.d/17295.bugfix
@@ -0,0 +1 @@
+Fix edge case in `/sync` returning the wrong the state when using sharded event persisters.
diff --git a/changelog.d/17296.feature b/changelog.d/17296.feature
new file mode 100644
index 0000000000..4ea5e7be85
--- /dev/null
+++ b/changelog.d/17296.feature
@@ -0,0 +1 @@
+Add support for the unstable [MSC4151](https://github.com/matrix-org/matrix-spec-proposals/pull/4151) report room API.
diff --git a/changelog.d/17297.misc b/changelog.d/17297.misc
new file mode 100644
index 0000000000..7ec351d2c1
--- /dev/null
+++ b/changelog.d/17297.misc
@@ -0,0 +1 @@
+Bump `mypy` from 1.8.0 to 1.9.0.
\ No newline at end of file
diff --git a/changelog.d/17300.misc b/changelog.d/17300.misc
new file mode 100644
index 0000000000..cdc40bb2e5
--- /dev/null
+++ b/changelog.d/17300.misc
@@ -0,0 +1 @@
+Expose the worker instance that persisted the event on `event.internal_metadata.instance_name`.
diff --git a/changelog.d/17301.bugfix b/changelog.d/17301.bugfix
new file mode 100644
index 0000000000..50383cb4a4
--- /dev/null
+++ b/changelog.d/17301.bugfix
@@ -0,0 +1 @@
+Add initial implementation of an experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint.
diff --git a/changelog.d/17308.doc b/changelog.d/17308.doc
new file mode 100644
index 0000000000..7ae080a684
--- /dev/null
+++ b/changelog.d/17308.doc
@@ -0,0 +1 @@
+Add missing quotes for example for `exclude_rooms_from_sync`.
diff --git a/changelog.d/17322.feature b/changelog.d/17322.feature
new file mode 100644
index 0000000000..85386c2df7
--- /dev/null
+++ b/changelog.d/17322.feature
@@ -0,0 +1 @@
+Add support for via query parameter from MSC415.
diff --git a/docker/complement/conf/workers-shared-extra.yaml.j2 b/docker/complement/conf/workers-shared-extra.yaml.j2
index 4c41ee7709..6588b3ce14 100644
--- a/docker/complement/conf/workers-shared-extra.yaml.j2
+++ b/docker/complement/conf/workers-shared-extra.yaml.j2
@@ -105,8 +105,6 @@ experimental_features:
   # Expose a room summary for public rooms
   msc3266_enabled: true
 
-  msc4115_membership_on_events: true
-
 server_notices:
   system_mxid_localpart: _server
   system_mxid_display_name: "Server Alert"
diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md
index 2c917d1f8e..22c545359d 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -1946,6 +1946,24 @@ Example configuration:
 max_image_pixels: 35M
 ```
 ---
+### `remote_media_download_burst_count`
+
+Remote media downloads are ratelimited using a [leaky bucket algorithm](https://en.wikipedia.org/wiki/Leaky_bucket), where a given "bucket" is keyed to the IP address of the requester when requesting remote media downloads. This configuration option sets the size of the bucket against which the size in bytes of downloads are penalized - if the bucket is full, ie a given number of bytes have already been downloaded, further downloads will be denied until the bucket drains.  Defaults to 500MiB. See also `remote_media_download_per_second` which determines the rate at which the "bucket" is emptied and thus has available space to authorize new requests.  
+
+Example configuration:
+```yaml
+remote_media_download_burst_count: 200M
+```
+---
+### `remote_media_download_per_second`
+
+Works in conjunction with `remote_media_download_burst_count` to ratelimit remote media downloads - this configuration option determines the rate at which the "bucket" (see above) leaks in bytes per second. As requests are made to download remote media, the size of those requests in bytes is added to the bucket, and once the bucket has reached it's capacity, no more requests will be allowed until a number of bytes has "drained" from the bucket. This setting determines the rate at which bytes drain from the bucket, with the practical effect that the larger the number, the faster the bucket leaks, allowing for more bytes downloaded over a shorter period of time. Defaults to 87KiB per second. See also `remote_media_download_burst_count`.
+
+Example configuration:
+```yaml
+remote_media_download_per_second: 40K
+```
+---
 ### `prevent_media_downloads_from`
 
 A list of domains to never download media from. Media from these
@@ -4132,7 +4150,7 @@ By default, no room is excluded.
 Example configuration:
 ```yaml
 exclude_rooms_from_sync:
-    - !foo:example.com
+    - "!foo:example.com"
 ```
 
 ---
diff --git a/poetry.lock b/poetry.lock
index 80924ccbb1..58981ff6e1 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -912,13 +912,13 @@ trio = ["async_generator", "trio"]
 
 [[package]]
 name = "jinja2"
-version = "3.1.3"
+version = "3.1.4"
 description = "A very fast and expressive template engine."
 optional = false
 python-versions = ">=3.7"
 files = [
-    {file = "Jinja2-3.1.3-py3-none-any.whl", hash = "sha256:7d6d50dd97d52cbc355597bd845fabfbac3f551e1f99619e39a35ce8c370b5fa"},
-    {file = "Jinja2-3.1.3.tar.gz", hash = "sha256:ac8bd6544d4bb2c9792bf3a159e80bba8fda7f07e81bc3aed565432d5925ba90"},
+    {file = "jinja2-3.1.4-py3-none-any.whl", hash = "sha256:bc5dd2abb727a5319567b7a813e6a2e7318c39f4f487cfe6c89c6f9c7d25197d"},
+    {file = "jinja2-3.1.4.tar.gz", hash = "sha256:4a3aee7acbbe7303aede8e9648d13b8bf88a429282aa6122a993f0ac800cb369"},
 ]
 
 [package.dependencies]
@@ -1319,103 +1319,103 @@ files = [
 
 [[package]]
 name = "msgpack"
-version = "1.0.7"
+version = "1.0.8"
 description = "MessagePack serializer"
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "msgpack-1.0.7-cp310-cp310-macosx_10_9_universal2.whl", hash = "sha256:04ad6069c86e531682f9e1e71b71c1c3937d6014a7c3e9edd2aa81ad58842862"},
-    {file = "msgpack-1.0.7-cp310-cp310-macosx_10_9_x86_64.whl", hash = "sha256:cca1b62fe70d761a282496b96a5e51c44c213e410a964bdffe0928e611368329"},
-    {file = "msgpack-1.0.7-cp310-cp310-macosx_11_0_arm64.whl", hash = "sha256:e50ebce52f41370707f1e21a59514e3375e3edd6e1832f5e5235237db933c98b"},
-    {file = "msgpack-1.0.7-cp310-cp310-manylinux_2_17_aarch64.manylinux2014_aarch64.whl", hash = "sha256:4a7b4f35de6a304b5533c238bee86b670b75b03d31b7797929caa7a624b5dda6"},
-    {file = "msgpack-1.0.7-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:28efb066cde83c479dfe5a48141a53bc7e5f13f785b92ddde336c716663039ee"},
-    {file = "msgpack-1.0.7-cp310-cp310-manylinux_2_5_i686.manylinux1_i686.manylinux_2_17_i686.manylinux2014_i686.whl", hash = "sha256:4cb14ce54d9b857be9591ac364cb08dc2d6a5c4318c1182cb1d02274029d590d"},
-    {file = "msgpack-1.0.7-cp310-cp310-musllinux_1_1_aarch64.whl", hash = "sha256:b573a43ef7c368ba4ea06050a957c2a7550f729c31f11dd616d2ac4aba99888d"},
-    {file = "msgpack-1.0.7-cp310-cp310-musllinux_1_1_i686.whl", hash = "sha256:ccf9a39706b604d884d2cb1e27fe973bc55f2890c52f38df742bc1d79ab9f5e1"},
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 ]
 
 [package.dependencies]
@@ -1524,13 +1524,13 @@ files = [
 
 [[package]]
 name = "phonenumbers"
-version = "8.13.37"
+version = "8.13.39"
 description = "Python version of Google's common library for parsing, formatting, storing and validating international phone numbers."
 optional = false
 python-versions = "*"
 files = [
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 ]
 
 [[package]]
@@ -2387,13 +2387,13 @@ doc = ["Sphinx", "sphinx-rtd-theme"]
 
 [[package]]
 name = "sentry-sdk"
-version = "2.1.1"
+version = "2.3.1"
 description = "Python client for Sentry (https://sentry.io)"
 optional = true
 python-versions = ">=3.6"
 files = [
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 ]
 
 [package.dependencies]
@@ -2415,7 +2415,7 @@ django = ["django (>=1.8)"]
 falcon = ["falcon (>=1.4)"]
 fastapi = ["fastapi (>=0.79.0)"]
 flask = ["blinker (>=1.1)", "flask (>=0.11)", "markupsafe"]
-grpcio = ["grpcio (>=1.21.1)"]
+grpcio = ["grpcio (>=1.21.1)", "protobuf (>=3.8.0)"]
 httpx = ["httpx (>=0.16.0)"]
 huey = ["huey (>=2)"]
 huggingface-hub = ["huggingface-hub (>=0.22)"]
@@ -2808,13 +2808,13 @@ files = [
 
 [[package]]
 name = "types-jsonschema"
-version = "4.21.0.20240311"
+version = "4.22.0.20240610"
 description = "Typing stubs for jsonschema"
 optional = false
 python-versions = ">=3.8"
 files = [
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 ]
 
 [package.dependencies]
@@ -2822,13 +2822,13 @@ referencing = "*"
 
 [[package]]
 name = "types-netaddr"
-version = "1.2.0.20240219"
+version = "1.3.0.20240530"
 description = "Typing stubs for netaddr"
 optional = false
 python-versions = ">=3.8"
 files = [
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 ]
 
 [[package]]
@@ -2844,13 +2844,13 @@ files = [
 
 [[package]]
 name = "types-pillow"
-version = "10.2.0.20240423"
+version = "10.2.0.20240520"
 description = "Typing stubs for Pillow"
 optional = false
 python-versions = ">=3.8"
 files = [
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+    {file = "types-Pillow-10.2.0.20240520.tar.gz", hash = "sha256:130b979195465fa1e1676d8e81c9c7c30319e8e95b12fae945e8f0d525213107"},
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 ]
 
 [[package]]
@@ -2881,13 +2881,13 @@ types-cffi = "*"
 
 [[package]]
 name = "types-pyyaml"
-version = "6.0.12.12"
+version = "6.0.12.20240311"
 description = "Typing stubs for PyYAML"
 optional = false
-python-versions = "*"
+python-versions = ">=3.8"
 files = [
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+    {file = "types-PyYAML-6.0.12.20240311.tar.gz", hash = "sha256:a9e0f0f88dc835739b0c1ca51ee90d04ca2a897a71af79de9aec5f38cb0a5342"},
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 ]
 
 [[package]]
diff --git a/rust/src/events/internal_metadata.rs b/rust/src/events/internal_metadata.rs
index 63774fbd54..ad87825f16 100644
--- a/rust/src/events/internal_metadata.rs
+++ b/rust/src/events/internal_metadata.rs
@@ -204,6 +204,8 @@ pub struct EventInternalMetadata {
     /// The stream ordering of this event. None, until it has been persisted.
     #[pyo3(get, set)]
     stream_ordering: Option<NonZeroI64>,
+    #[pyo3(get, set)]
+    instance_name: Option<String>,
 
     /// whether this event is an outlier (ie, whether we have the state at that
     /// point in the DAG)
@@ -232,6 +234,7 @@ impl EventInternalMetadata {
         Ok(EventInternalMetadata {
             data,
             stream_ordering: None,
+            instance_name: None,
             outlier: false,
         })
     }
diff --git a/scripts-dev/complement.sh b/scripts-dev/complement.sh
index b306b80749..4ad547bc7e 100755
--- a/scripts-dev/complement.sh
+++ b/scripts-dev/complement.sh
@@ -223,7 +223,6 @@ test_packages=(
     ./tests/msc3930
     ./tests/msc3902
     ./tests/msc3967
-    ./tests/msc4115
 )
 
 # Enable dirty runs, so tests will reuse the same container where possible.
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 0a9123c56b..9265a271d2 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -50,7 +50,7 @@ class Membership:
     KNOCK: Final = "knock"
     LEAVE: Final = "leave"
     BAN: Final = "ban"
-    LIST: Final = (INVITE, JOIN, KNOCK, LEAVE, BAN)
+    LIST: Final = {INVITE, JOIN, KNOCK, LEAVE, BAN}
 
 
 class PresenceState:
@@ -238,7 +238,7 @@ class EventUnsignedContentFields:
     """Fields found inside the 'unsigned' data on events"""
 
     # Requesting user's membership, per MSC4115
-    MSC4115_MEMBERSHIP: Final = "io.element.msc4115.membership"
+    MEMBERSHIP: Final = "membership"
 
 
 class RoomTypes:
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index 75fe6d7b24..23e96da6a3 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -393,9 +393,6 @@ class ExperimentalConfig(Config):
         # MSC3391: Removing account data.
         self.msc3391_enabled = experimental.get("msc3391_enabled", False)
 
-        # MSC3967: Do not require UIA when first uploading cross signing keys
-        self.msc3967_enabled = experimental.get("msc3967_enabled", False)
-
         # MSC3861: Matrix architecture change to delegate authentication via OIDC
         try:
             self.msc3861 = MSC3861(**experimental.get("msc3861", {}))
@@ -436,10 +433,12 @@ class ExperimentalConfig(Config):
                 ("experimental", "msc4108_delegation_endpoint"),
             )
 
-        self.msc4115_membership_on_events = experimental.get(
-            "msc4115_membership_on_events", False
-        )
-
         self.msc3916_authenticated_media_enabled = experimental.get(
             "msc3916_authenticated_media_enabled", False
         )
+
+        # MSC4151: Report room API (Client-Server API)
+        self.msc4151_enabled: bool = experimental.get("msc4151_enabled", False)
+
+        # MSC4156: Migrate server_name to via
+        self.msc4156_enabled: bool = experimental.get("msc4156_enabled", False)
diff --git a/synapse/config/ratelimiting.py b/synapse/config/ratelimiting.py
index d2cb4576df..3fa33f5373 100644
--- a/synapse/config/ratelimiting.py
+++ b/synapse/config/ratelimiting.py
@@ -218,3 +218,13 @@ class RatelimitConfig(Config):
             "rc_media_create",
             defaults={"per_second": 10, "burst_count": 50},
         )
+
+        self.remote_media_downloads = RatelimitSettings(
+            key="rc_remote_media_downloads",
+            per_second=self.parse_size(
+                config.get("remote_media_download_per_second", "87K")
+            ),
+            burst_count=self.parse_size(
+                config.get("remote_media_download_burst_count", "500M")
+            ),
+        )
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 0772472312..b997d82d71 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -90,6 +90,7 @@ def prune_event(event: EventBase) -> EventBase:
     pruned_event.internal_metadata.stream_ordering = (
         event.internal_metadata.stream_ordering
     )
+    pruned_event.internal_metadata.instance_name = event.internal_metadata.instance_name
     pruned_event.internal_metadata.outlier = event.internal_metadata.outlier
 
     # Mark the event as redacted
@@ -116,6 +117,7 @@ def clone_event(event: EventBase) -> EventBase:
     new_event.internal_metadata.stream_ordering = (
         event.internal_metadata.stream_ordering
     )
+    new_event.internal_metadata.instance_name = event.internal_metadata.instance_name
     new_event.internal_metadata.outlier = event.internal_metadata.outlier
 
     return new_event
diff --git a/synapse/events/validator.py b/synapse/events/validator.py
index 62f0b67dbd..73b63b77f2 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -47,9 +47,9 @@ from synapse.events.utils import (
     validate_canonicaljson,
 )
 from synapse.http.servlet import validate_json_object
-from synapse.rest.models import RequestBodyModel
 from synapse.storage.controllers.state import server_acl_evaluator_from_event
 from synapse.types import EventID, JsonDict, RoomID, StrCollection, UserID
+from synapse.types.rest import RequestBodyModel
 
 
 class EventValidator:
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index e613eb87a6..f0f5a37a57 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -56,6 +56,7 @@ from synapse.api.errors import (
     SynapseError,
     UnsupportedRoomVersionError,
 )
+from synapse.api.ratelimiting import Ratelimiter
 from synapse.api.room_versions import (
     KNOWN_ROOM_VERSIONS,
     EventFormatVersions,
@@ -1877,6 +1878,8 @@ class FederationClient(FederationBase):
         output_stream: BinaryIO,
         max_size: int,
         max_timeout_ms: int,
+        download_ratelimiter: Ratelimiter,
+        ip_address: str,
     ) -> Tuple[int, Dict[bytes, List[bytes]]]:
         try:
             return await self.transport_layer.download_media_v3(
@@ -1885,6 +1888,8 @@ class FederationClient(FederationBase):
                 output_stream=output_stream,
                 max_size=max_size,
                 max_timeout_ms=max_timeout_ms,
+                download_ratelimiter=download_ratelimiter,
+                ip_address=ip_address,
             )
         except HttpResponseException as e:
             # If an error is received that is due to an unrecognised endpoint,
@@ -1905,6 +1910,8 @@ class FederationClient(FederationBase):
             output_stream=output_stream,
             max_size=max_size,
             max_timeout_ms=max_timeout_ms,
+            download_ratelimiter=download_ratelimiter,
+            ip_address=ip_address,
         )
 
 
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 7ffc650aa1..1932fa82a4 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -674,7 +674,7 @@ class FederationServer(FederationBase):
         # This is in addition to the HS-level rate limiting applied by
         # BaseFederationServlet.
         # type-ignore: mypy doesn't seem able to deduce the type of the limiter(!?)
-        await self._room_member_handler._join_rate_per_room_limiter.ratelimit(  # type: ignore[has-type]
+        await self._room_member_handler._join_rate_per_room_limiter.ratelimit(
             requester=None,
             key=room_id,
             update=False,
@@ -717,7 +717,7 @@ class FederationServer(FederationBase):
             SynapseTags.SEND_JOIN_RESPONSE_IS_PARTIAL_STATE,
             caller_supports_partial_state,
         )
-        await self._room_member_handler._join_rate_per_room_limiter.ratelimit(  # type: ignore[has-type]
+        await self._room_member_handler._join_rate_per_room_limiter.ratelimit(
             requester=None,
             key=room_id,
             update=False,
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index de408f7f8d..af1336fe5f 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -43,6 +43,7 @@ import ijson
 
 from synapse.api.constants import Direction, Membership
 from synapse.api.errors import Codes, HttpResponseException, SynapseError
+from synapse.api.ratelimiting import Ratelimiter
 from synapse.api.room_versions import RoomVersion
 from synapse.api.urls import (
     FEDERATION_UNSTABLE_PREFIX,
@@ -819,6 +820,8 @@ class TransportLayerClient:
         output_stream: BinaryIO,
         max_size: int,
         max_timeout_ms: int,
+        download_ratelimiter: Ratelimiter,
+        ip_address: str,
     ) -> Tuple[int, Dict[bytes, List[bytes]]]:
         path = f"/_matrix/media/r0/download/{destination}/{media_id}"
 
@@ -834,6 +837,8 @@ class TransportLayerClient:
                 "allow_remote": "false",
                 "timeout_ms": str(max_timeout_ms),
             },
+            download_ratelimiter=download_ratelimiter,
+            ip_address=ip_address,
         )
 
     async def download_media_v3(
@@ -843,6 +848,8 @@ class TransportLayerClient:
         output_stream: BinaryIO,
         max_size: int,
         max_timeout_ms: int,
+        download_ratelimiter: Ratelimiter,
+        ip_address: str,
     ) -> Tuple[int, Dict[bytes, List[bytes]]]:
         path = f"/_matrix/media/v3/download/{destination}/{media_id}"
 
@@ -862,6 +869,8 @@ class TransportLayerClient:
                 "allow_redirect": "true",
             },
             follow_redirects=True,
+            download_ratelimiter=download_ratelimiter,
+            ip_address=ip_address,
         )
 
 
diff --git a/synapse/federation/transport/server/__init__.py b/synapse/federation/transport/server/__init__.py
index bac569e977..266675c9b8 100644
--- a/synapse/federation/transport/server/__init__.py
+++ b/synapse/federation/transport/server/__init__.py
@@ -19,6 +19,7 @@
 # [This file includes modifications made by New Vector Limited]
 #
 #
+import inspect
 import logging
 from typing import TYPE_CHECKING, Dict, Iterable, List, Optional, Tuple, Type
 
@@ -33,6 +34,7 @@ from synapse.federation.transport.server.federation import (
     FEDERATION_SERVLET_CLASSES,
     FederationAccountStatusServlet,
     FederationUnstableClientKeysClaimServlet,
+    FederationUnstableMediaDownloadServlet,
 )
 from synapse.http.server import HttpServer, JsonResource
 from synapse.http.servlet import (
@@ -315,6 +317,28 @@ def register_servlets(
             ):
                 continue
 
+            if servletclass == FederationUnstableMediaDownloadServlet:
+                if (
+                    not hs.config.server.enable_media_repo
+                    or not hs.config.experimental.msc3916_authenticated_media_enabled
+                ):
+                    continue
+
+                # don't load the endpoint if the storage provider is incompatible
+                media_repo = hs.get_media_repository()
+                load_download_endpoint = True
+                for provider in media_repo.media_storage.storage_providers:
+                    signature = inspect.signature(provider.backend.fetch)
+                    if "federation" not in signature.parameters:
+                        logger.warning(
+                            f"Federation media `/download` endpoint will not be enabled as storage provider {provider.backend} is not compatible with this endpoint."
+                        )
+                        load_download_endpoint = False
+                        break
+
+                if not load_download_endpoint:
+                    continue
+
             servletclass(
                 hs=hs,
                 authenticator=authenticator,
diff --git a/synapse/federation/transport/server/_base.py b/synapse/federation/transport/server/_base.py
index db0f5076a9..4e2717b565 100644
--- a/synapse/federation/transport/server/_base.py
+++ b/synapse/federation/transport/server/_base.py
@@ -360,13 +360,29 @@ class BaseFederationServlet:
                                     "request"
                                 )
                                 return None
+                            if (
+                                func.__self__.__class__.__name__  # type: ignore
+                                == "FederationUnstableMediaDownloadServlet"
+                            ):
+                                response = await func(
+                                    origin, content, request, *args, **kwargs
+                                )
+                            else:
+                                response = await func(
+                                    origin, content, request.args, *args, **kwargs
+                                )
+                    else:
+                        if (
+                            func.__self__.__class__.__name__  # type: ignore
+                            == "FederationUnstableMediaDownloadServlet"
+                        ):
+                            response = await func(
+                                origin, content, request, *args, **kwargs
+                            )
+                        else:
                             response = await func(
                                 origin, content, request.args, *args, **kwargs
                             )
-                    else:
-                        response = await func(
-                            origin, content, request.args, *args, **kwargs
-                        )
             finally:
                 # if we used the origin's context as the parent, add a new span using
                 # the servlet span as a parent, so that we have a link
diff --git a/synapse/federation/transport/server/federation.py b/synapse/federation/transport/server/federation.py
index a59734785f..1f02451efa 100644
--- a/synapse/federation/transport/server/federation.py
+++ b/synapse/federation/transport/server/federation.py
@@ -44,10 +44,13 @@ from synapse.federation.transport.server._base import (
 )
 from synapse.http.servlet import (
     parse_boolean_from_args,
+    parse_integer,
     parse_integer_from_args,
     parse_string_from_args,
     parse_strings_from_args,
 )
+from synapse.http.site import SynapseRequest
+from synapse.media._base import DEFAULT_MAX_TIMEOUT_MS, MAXIMUM_ALLOWED_MAX_TIMEOUT_MS
 from synapse.types import JsonDict
 from synapse.util import SYNAPSE_VERSION
 from synapse.util.ratelimitutils import FederationRateLimiter
@@ -787,6 +790,43 @@ class FederationAccountStatusServlet(BaseFederationServerServlet):
         return 200, {"account_statuses": statuses, "failures": failures}
 
 
+class FederationUnstableMediaDownloadServlet(BaseFederationServerServlet):
+    """
+    Implementation of new federation media `/download` endpoint outlined in MSC3916. Returns
+    a multipart/form-data response consisting of a JSON object and the requested media
+    item. This endpoint only returns local media.
+    """
+
+    PATH = "/media/download/(?P<media_id>[^/]*)"
+    PREFIX = FEDERATION_UNSTABLE_PREFIX + "/org.matrix.msc3916"
+    RATELIMIT = True
+
+    def __init__(
+        self,
+        hs: "HomeServer",
+        ratelimiter: FederationRateLimiter,
+        authenticator: Authenticator,
+        server_name: str,
+    ):
+        super().__init__(hs, authenticator, ratelimiter, server_name)
+        self.media_repo = self.hs.get_media_repository()
+
+    async def on_GET(
+        self,
+        origin: Optional[str],
+        content: Literal[None],
+        request: SynapseRequest,
+        media_id: str,
+    ) -> None:
+        max_timeout_ms = parse_integer(
+            request, "timeout_ms", default=DEFAULT_MAX_TIMEOUT_MS
+        )
+        max_timeout_ms = min(max_timeout_ms, MAXIMUM_ALLOWED_MAX_TIMEOUT_MS)
+        await self.media_repo.get_local_media(
+            request, media_id, None, max_timeout_ms, federation=True
+        )
+
+
 FEDERATION_SERVLET_CLASSES: Tuple[Type[BaseFederationServlet], ...] = (
     FederationSendServlet,
     FederationEventServlet,
@@ -818,4 +858,5 @@ FEDERATION_SERVLET_CLASSES: Tuple[Type[BaseFederationServlet], ...] = (
     FederationV1SendKnockServlet,
     FederationMakeKnockServlet,
     FederationAccountStatusServlet,
+    FederationUnstableMediaDownloadServlet,
 )
diff --git a/synapse/handlers/admin.py b/synapse/handlers/admin.py
index 702d40332c..ec35784c5f 100644
--- a/synapse/handlers/admin.py
+++ b/synapse/handlers/admin.py
@@ -42,7 +42,6 @@ class AdminHandler:
         self._device_handler = hs.get_device_handler()
         self._storage_controllers = hs.get_storage_controllers()
         self._state_storage_controller = self._storage_controllers.state
-        self._hs_config = hs.config
         self._msc3866_enabled = hs.config.experimental.msc3866.enabled
 
     async def get_whois(self, user: UserID) -> JsonMapping:
@@ -126,13 +125,7 @@ class AdminHandler:
         # Get all rooms the user is in or has been in
         rooms = await self._store.get_rooms_for_local_user_where_membership_is(
             user_id,
-            membership_list=(
-                Membership.JOIN,
-                Membership.LEAVE,
-                Membership.BAN,
-                Membership.INVITE,
-                Membership.KNOCK,
-            ),
+            membership_list=Membership.LIST,
         )
 
         # We only try and fetch events for rooms the user has been in. If
@@ -179,7 +172,7 @@ class AdminHandler:
             if room.membership == Membership.JOIN:
                 stream_ordering = self._store.get_room_max_stream_ordering()
             else:
-                stream_ordering = room.stream_ordering
+                stream_ordering = room.event_pos.stream
 
             from_key = RoomStreamToken(topological=0, stream=0)
             to_key = RoomStreamToken(stream=stream_ordering)
@@ -221,7 +214,6 @@ class AdminHandler:
                     self._storage_controllers,
                     user_id,
                     events,
-                    msc4115_membership_on_events=self._hs_config.experimental.msc4115_membership_on_events,
                 )
 
                 writer.write_events(room_id, events)
diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index 560530a7b3..668cec513b 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -35,6 +35,7 @@ from synapse.api.errors import CodeMessageException, Codes, NotFoundError, Synap
 from synapse.handlers.device import DeviceHandler
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.logging.opentracing import log_kv, set_tag, tag_args, trace
+from synapse.replication.http.devices import ReplicationUploadKeysForUserRestServlet
 from synapse.types import (
     JsonDict,
     JsonMapping,
@@ -45,7 +46,10 @@ from synapse.types import (
 from synapse.util import json_decoder
 from synapse.util.async_helpers import Linearizer, concurrently_execute
 from synapse.util.cancellation import cancellable
-from synapse.util.retryutils import NotRetryingDestination
+from synapse.util.retryutils import (
+    NotRetryingDestination,
+    filter_destinations_by_retry_limiter,
+)
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -86,6 +90,12 @@ class E2eKeysHandler:
                 edu_updater.incoming_signing_key_update,
             )
 
+            self.device_key_uploader = self.upload_device_keys_for_user
+        else:
+            self.device_key_uploader = (
+                ReplicationUploadKeysForUserRestServlet.make_client(hs)
+            )
+
         # doesn't really work as part of the generic query API, because the
         # query request requires an object POST, but we abuse the
         # "query handler" interface.
@@ -268,10 +278,8 @@ class E2eKeysHandler:
                 "%d destinations to query devices for", len(remote_queries_not_in_cache)
             )
 
-            async def _query(
-                destination_queries: Tuple[str, Dict[str, Iterable[str]]]
-            ) -> None:
-                destination, queries = destination_queries
+            async def _query(destination: str) -> None:
+                queries = remote_queries_not_in_cache[destination]
                 return await self._query_devices_for_destination(
                     results,
                     cross_signing_keys,
@@ -281,9 +289,20 @@ class E2eKeysHandler:
                     timeout,
                 )
 
+            # Only try and fetch keys for destinations that are not marked as
+            # down.
+            filtered_destinations = await filter_destinations_by_retry_limiter(
+                remote_queries_not_in_cache.keys(),
+                self.clock,
+                self.store,
+                # Let's give an arbitrary grace period for those hosts that are
+                # only recently down
+                retry_due_within_ms=60 * 1000,
+            )
+
             await concurrently_execute(
                 _query,
-                remote_queries_not_in_cache.items(),
+                filtered_destinations,
                 10,
                 delay_cancellation=True,
             )
@@ -784,36 +803,17 @@ class E2eKeysHandler:
             "one_time_keys": A mapping from algorithm to number of keys for that
                 algorithm, including those previously persisted.
         """
-        # This can only be called from the main process.
-        assert isinstance(self.device_handler, DeviceHandler)
-
         time_now = self.clock.time_msec()
 
         # TODO: Validate the JSON to make sure it has the right keys.
         device_keys = keys.get("device_keys", None)
         if device_keys:
-            logger.info(
-                "Updating device_keys for device %r for user %s at %d",
-                device_id,
-                user_id,
-                time_now,
+            await self.device_key_uploader(
+                user_id=user_id,
+                device_id=device_id,
+                keys={"device_keys": device_keys},
             )
-            log_kv(
-                {
-                    "message": "Updating device_keys for user.",
-                    "user_id": user_id,
-                    "device_id": device_id,
-                }
-            )
-            # TODO: Sign the JSON with the server key
-            changed = await self.store.set_e2e_device_keys(
-                user_id, device_id, time_now, device_keys
-            )
-            if changed:
-                # Only notify about device updates *if* the keys actually changed
-                await self.device_handler.notify_device_update(user_id, [device_id])
-        else:
-            log_kv({"message": "Not updating device_keys for user", "user_id": user_id})
+
         one_time_keys = keys.get("one_time_keys", None)
         if one_time_keys:
             log_kv(
@@ -849,6 +849,49 @@ class E2eKeysHandler:
                 {"message": "Did not update fallback_keys", "reason": "no keys given"}
             )
 
+        result = await self.store.count_e2e_one_time_keys(user_id, device_id)
+
+        set_tag("one_time_key_counts", str(result))
+        return {"one_time_key_counts": result}
+
+    @tag_args
+    async def upload_device_keys_for_user(
+        self, user_id: str, device_id: str, keys: JsonDict
+    ) -> None:
+        """
+        Args:
+            user_id: user whose keys are being uploaded.
+            device_id: device whose keys are being uploaded.
+            device_keys: the `device_keys` of an /keys/upload request.
+
+        """
+        # This can only be called from the main process.
+        assert isinstance(self.device_handler, DeviceHandler)
+
+        time_now = self.clock.time_msec()
+
+        device_keys = keys["device_keys"]
+        logger.info(
+            "Updating device_keys for device %r for user %s at %d",
+            device_id,
+            user_id,
+            time_now,
+        )
+        log_kv(
+            {
+                "message": "Updating device_keys for user.",
+                "user_id": user_id,
+                "device_id": device_id,
+            }
+        )
+        # TODO: Sign the JSON with the server key
+        changed = await self.store.set_e2e_device_keys(
+            user_id, device_id, time_now, device_keys
+        )
+        if changed:
+            # Only notify about device updates *if* the keys actually changed
+            await self.device_handler.notify_device_update(user_id, [device_id])
+
         # the device should have been registered already, but it may have been
         # deleted due to a race with a DELETE request. Or we may be using an
         # old access_token without an associated device_id. Either way, we
@@ -856,11 +899,6 @@ class E2eKeysHandler:
         # keys without a corresponding device.
         await self.device_handler.check_device_registered(user_id, device_id)
 
-        result = await self.store.count_e2e_one_time_keys(user_id, device_id)
-
-        set_tag("one_time_key_counts", str(result))
-        return {"one_time_key_counts": result}
-
     async def _upload_one_time_keys_for_user(
         self, user_id: str, device_id: str, time_now: int, one_time_keys: JsonDict
     ) -> None:
diff --git a/synapse/handlers/e2e_room_keys.py b/synapse/handlers/e2e_room_keys.py
index e76a51ba30..99f9f6e64a 100644
--- a/synapse/handlers/e2e_room_keys.py
+++ b/synapse/handlers/e2e_room_keys.py
@@ -247,6 +247,12 @@ class E2eRoomKeysHandler:
                     if current_room_key:
                         if self._should_replace_room_key(current_room_key, room_key):
                             log_kv({"message": "Replacing room key."})
+                            logger.debug(
+                                "Replacing room key. room=%s session=%s user=%s",
+                                room_id,
+                                session_id,
+                                user_id,
+                            )
                             # updates are done one at a time in the DB, so send
                             # updates right away rather than batching them up,
                             # like we do with the inserts
@@ -256,6 +262,12 @@ class E2eRoomKeysHandler:
                             changed = True
                         else:
                             log_kv({"message": "Not replacing room_key."})
+                            logger.debug(
+                                "Not replacing room key. room=%s session=%s user=%s",
+                                room_id,
+                                session_id,
+                                user_id,
+                            )
                     else:
                         log_kv(
                             {
@@ -265,6 +277,12 @@ class E2eRoomKeysHandler:
                             }
                         )
                         log_kv({"message": "Replacing room key."})
+                        logger.debug(
+                            "Inserting new room key. room=%s session=%s user=%s",
+                            room_id,
+                            session_id,
+                            user_id,
+                        )
                         to_insert.append((room_id, session_id, room_key))
                         changed = True
 
diff --git a/synapse/handlers/events.py b/synapse/handlers/events.py
index 09d553cff1..3f46032a43 100644
--- a/synapse/handlers/events.py
+++ b/synapse/handlers/events.py
@@ -148,7 +148,6 @@ class EventHandler:
     def __init__(self, hs: "HomeServer"):
         self.store = hs.get_datastores().main
         self._storage_controllers = hs.get_storage_controllers()
-        self._config = hs.config
 
     async def get_event(
         self,
@@ -194,7 +193,6 @@ class EventHandler:
             user.to_string(),
             [event],
             is_peeking=is_peeking,
-            msc4115_membership_on_events=self._config.experimental.msc4115_membership_on_events,
         )
 
         if not filtered:
diff --git a/synapse/handlers/initial_sync.py b/synapse/handlers/initial_sync.py
index d99fc4bec0..bd3c87f5f4 100644
--- a/synapse/handlers/initial_sync.py
+++ b/synapse/handlers/initial_sync.py
@@ -199,7 +199,7 @@ class InitialSyncHandler:
                     )
                 elif event.membership == Membership.LEAVE:
                     room_end_token = RoomStreamToken(
-                        stream=event.stream_ordering,
+                        stream=event.event_pos.stream,
                     )
                     deferred_room_state = run_in_background(
                         self._state_storage_controller.get_state_for_events,
@@ -224,7 +224,6 @@ class InitialSyncHandler:
                     self._storage_controllers,
                     user_id,
                     messages,
-                    msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
                 )
 
                 start_token = now_token.copy_and_replace(StreamKeyType.ROOM, token)
@@ -383,7 +382,6 @@ class InitialSyncHandler:
             requester.user.to_string(),
             messages,
             is_peeking=is_peeking,
-            msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
         )
 
         start_token = StreamToken.START.copy_and_replace(StreamKeyType.ROOM, token)
@@ -498,7 +496,6 @@ class InitialSyncHandler:
             requester.user.to_string(),
             messages,
             is_peeking=is_peeking,
-            msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
         )
 
         start_token = now_token.copy_and_replace(StreamKeyType.ROOM, token)
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index de5bd44a5f..16d01efc67 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -201,7 +201,7 @@ class MessageHandler:
 
         if at_token:
             last_event_id = (
-                await self.store.get_last_event_in_room_before_stream_ordering(
+                await self.store.get_last_event_id_in_room_before_stream_ordering(
                     room_id,
                     end_token=at_token.room_key,
                 )
@@ -1551,6 +1551,7 @@ class EventCreationHandler:
                     # stream_ordering entry manually (as it was persisted on
                     # another worker).
                     event.internal_metadata.stream_ordering = stream_id
+                    event.internal_metadata.instance_name = writer_instance
 
                 return event
 
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index 6617105cdb..872c85fbad 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -27,7 +27,6 @@ from synapse.api.constants import Direction, EventTypes, Membership
 from synapse.api.errors import SynapseError
 from synapse.api.filtering import Filter
 from synapse.events.utils import SerializeEventConfig
-from synapse.handlers.room import ShutdownRoomParams, ShutdownRoomResponse
 from synapse.handlers.worker_lock import NEW_EVENT_DURING_PURGE_LOCK_NAME
 from synapse.logging.opentracing import trace
 from synapse.metrics.background_process_metrics import run_as_background_process
@@ -41,6 +40,7 @@ from synapse.types import (
     StreamKeyType,
     TaskStatus,
 )
+from synapse.types.handlers import ShutdownRoomParams, ShutdownRoomResponse
 from synapse.types.state import StateFilter
 from synapse.util.async_helpers import ReadWriteLock
 from synapse.visibility import filter_events_for_client
@@ -623,7 +623,6 @@ class PaginationHandler:
                 user_id,
                 events,
                 is_peeking=(member_event_id is None),
-                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
         # if after the filter applied there are no more events
diff --git a/synapse/handlers/relations.py b/synapse/handlers/relations.py
index de092f8623..efe31e81f9 100644
--- a/synapse/handlers/relations.py
+++ b/synapse/handlers/relations.py
@@ -95,7 +95,6 @@ class RelationsHandler:
         self._event_handler = hs.get_event_handler()
         self._event_serializer = hs.get_event_client_serializer()
         self._event_creation_handler = hs.get_event_creation_handler()
-        self._config = hs.config
 
     async def get_relations(
         self,
@@ -164,7 +163,6 @@ class RelationsHandler:
             user_id,
             events,
             is_peeking=(member_event_id is None),
-            msc4115_membership_on_events=self._config.experimental.msc4115_membership_on_events,
         )
 
         # The relations returned for the requested event do include their
@@ -610,7 +608,6 @@ class RelationsHandler:
             user_id,
             events,
             is_peeking=(member_event_id is None),
-            msc4115_membership_on_events=self._config.experimental.msc4115_membership_on_events,
         )
 
         aggregations = await self.get_bundled_aggregations(
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 51739a2653..2302d283a7 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -40,7 +40,6 @@ from typing import (
 )
 
 import attr
-from typing_extensions import TypedDict
 
 import synapse.events.snapshot
 from synapse.api.constants import (
@@ -88,6 +87,7 @@ from synapse.types import (
     UserID,
     create_requester,
 )
+from synapse.types.handlers import ShutdownRoomParams, ShutdownRoomResponse
 from synapse.types.state import StateFilter
 from synapse.util import stringutils
 from synapse.util.caches.response_cache import ResponseCache
@@ -1476,7 +1476,6 @@ class RoomContextHandler:
                 user.to_string(),
                 events,
                 is_peeking=is_peeking,
-                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
         event = await self.store.get_event(
@@ -1780,63 +1779,6 @@ class RoomEventSource(EventSource[RoomStreamToken, EventBase]):
         return self.store.get_current_room_stream_token_for_room_id(room_id)
 
 
-class ShutdownRoomParams(TypedDict):
-    """
-    Attributes:
-        requester_user_id:
-            User who requested the action. Will be recorded as putting the room on the
-            blocking list.
-        new_room_user_id:
-            If set, a new room will be created with this user ID
-            as the creator and admin, and all users in the old room will be
-            moved into that room. If not set, no new room will be created
-            and the users will just be removed from the old room.
-        new_room_name:
-            A string representing the name of the room that new users will
-            be invited to. Defaults to `Content Violation Notification`
-        message:
-            A string containing the first message that will be sent as
-            `new_room_user_id` in the new room. Ideally this will clearly
-            convey why the original room was shut down.
-            Defaults to `Sharing illegal content on this server is not
-            permitted and rooms in violation will be blocked.`
-        block:
-            If set to `true`, this room will be added to a blocking list,
-            preventing future attempts to join the room. Defaults to `false`.
-        purge:
-            If set to `true`, purge the given room from the database.
-        force_purge:
-            If set to `true`, the room will be purged from database
-            even if there are still users joined to the room.
-    """
-
-    requester_user_id: Optional[str]
-    new_room_user_id: Optional[str]
-    new_room_name: Optional[str]
-    message: Optional[str]
-    block: bool
-    purge: bool
-    force_purge: bool
-
-
-class ShutdownRoomResponse(TypedDict):
-    """
-    Attributes:
-        kicked_users: An array of users (`user_id`) that were kicked.
-        failed_to_kick_users:
-            An array of users (`user_id`) that that were not kicked.
-        local_aliases:
-            An array of strings representing the local aliases that were
-            migrated from the old room to the new.
-        new_room_id: A string representing the room ID of the new room.
-    """
-
-    kicked_users: List[str]
-    failed_to_kick_users: List[str]
-    local_aliases: List[str]
-    new_room_id: Optional[str]
-
-
 class RoomShutdownHandler:
     DEFAULT_MESSAGE = (
         "Sharing illegal content on this server is not permitted and rooms in"
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index fdbe98de3b..a7d52fa648 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -483,7 +483,6 @@ class SearchHandler:
             self._storage_controllers,
             user.to_string(),
             filtered_events,
-            msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
         )
 
         events.sort(key=lambda e: -rank_map[e.event_id])
@@ -585,7 +584,6 @@ class SearchHandler:
                 self._storage_controllers,
                 user.to_string(),
                 filtered_events,
-                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
             room_events.extend(events)
@@ -673,14 +671,12 @@ class SearchHandler:
                 self._storage_controllers,
                 user.to_string(),
                 res.events_before,
-                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
             events_after = await filter_events_for_client(
                 self._storage_controllers,
                 user.to_string(),
                 res.events_after,
-                msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
             )
 
             context: JsonDict = {
diff --git a/synapse/handlers/sliding_sync.py b/synapse/handlers/sliding_sync.py
new file mode 100644
index 0000000000..16d94925f5
--- /dev/null
+++ b/synapse/handlers/sliding_sync.py
@@ -0,0 +1,667 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2024 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# Originally licensed under the Apache License, Version 2.0:
+# <http://www.apache.org/licenses/LICENSE-2.0>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+import logging
+from typing import TYPE_CHECKING, Dict, List, Optional, Tuple
+
+from immutabledict import immutabledict
+
+from synapse.api.constants import AccountDataTypes, EventTypes, Membership
+from synapse.events import EventBase
+from synapse.storage.roommember import RoomsForUser
+from synapse.types import (
+    PersistedEventPosition,
+    Requester,
+    RoomStreamToken,
+    StreamToken,
+    UserID,
+)
+from synapse.types.handlers import OperationType, SlidingSyncConfig, SlidingSyncResult
+from synapse.types.state import StateFilter
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+def convert_event_to_rooms_for_user(event: EventBase) -> RoomsForUser:
+    """
+    Quick helper to convert an event to a `RoomsForUser` object.
+    """
+    # These fields should be present for all persisted events
+    assert event.internal_metadata.stream_ordering is not None
+    assert event.internal_metadata.instance_name is not None
+
+    return RoomsForUser(
+        room_id=event.room_id,
+        sender=event.sender,
+        membership=event.membership,
+        event_id=event.event_id,
+        event_pos=PersistedEventPosition(
+            event.internal_metadata.instance_name,
+            event.internal_metadata.stream_ordering,
+        ),
+        room_version_id=event.room_version.identifier,
+    )
+
+
+def filter_membership_for_sync(*, membership: str, user_id: str, sender: str) -> bool:
+    """
+    Returns True if the membership event should be included in the sync response,
+    otherwise False.
+
+    Attributes:
+        membership: The membership state of the user in the room.
+        user_id: The user ID that the membership applies to
+        sender: The person who sent the membership event
+    """
+
+    # Everything except `Membership.LEAVE` because we want everything that's *still*
+    # relevant to the user. There are few more things to include in the sync response
+    # (newly_left) but those are handled separately.
+    #
+    # This logic includes kicks (leave events where the sender is not the same user) and
+    # can be read as "anything that isn't a leave or a leave with a different sender".
+    return membership != Membership.LEAVE or sender != user_id
+
+
+class SlidingSyncHandler:
+    def __init__(self, hs: "HomeServer"):
+        self.clock = hs.get_clock()
+        self.store = hs.get_datastores().main
+        self.storage_controllers = hs.get_storage_controllers()
+        self.auth_blocking = hs.get_auth_blocking()
+        self.notifier = hs.get_notifier()
+        self.event_sources = hs.get_event_sources()
+        self.rooms_to_exclude_globally = hs.config.server.rooms_to_exclude_from_sync
+
+    async def wait_for_sync_for_user(
+        self,
+        requester: Requester,
+        sync_config: SlidingSyncConfig,
+        from_token: Optional[StreamToken] = None,
+        timeout_ms: int = 0,
+    ) -> SlidingSyncResult:
+        """
+        Get the sync for a client if we have new data for it now. Otherwise
+        wait for new data to arrive on the server. If the timeout expires, then
+        return an empty sync result.
+
+        Args:
+            requester: The user making the request
+            sync_config: Sync configuration
+            from_token: The point in the stream to sync from. Token of the end of the
+                previous batch. May be `None` if this is the initial sync request.
+            timeout_ms: The time in milliseconds to wait for new data to arrive. If 0,
+                we will immediately but there might not be any new data so we just return an
+                empty response.
+        """
+        # If the user is not part of the mau group, then check that limits have
+        # not been exceeded (if not part of the group by this point, almost certain
+        # auth_blocking will occur)
+        await self.auth_blocking.check_auth_blocking(requester=requester)
+
+        # TODO: If the To-Device extension is enabled and we have a `from_token`, delete
+        # any to-device messages before that token (since we now know that the device
+        # has received them). (see sync v2 for how to do this)
+
+        # If we're working with a user-provided token, we need to make sure to wait for
+        # this worker to catch up with the token so we don't skip past any incoming
+        # events or future events if the user is nefariously, manually modifying the
+        # token.
+        if from_token is not None:
+            # We need to make sure this worker has caught up with the token. If
+            # this returns false, it means we timed out waiting, and we should
+            # just return an empty response.
+            before_wait_ts = self.clock.time_msec()
+            if not await self.notifier.wait_for_stream_token(from_token):
+                logger.warning(
+                    "Timed out waiting for worker to catch up. Returning empty response"
+                )
+                return SlidingSyncResult.empty(from_token)
+
+            # If we've spent significant time waiting to catch up, take it off
+            # the timeout.
+            after_wait_ts = self.clock.time_msec()
+            if after_wait_ts - before_wait_ts > 1_000:
+                timeout_ms -= after_wait_ts - before_wait_ts
+                timeout_ms = max(timeout_ms, 0)
+
+        # We're going to respond immediately if the timeout is 0 or if this is an
+        # initial sync (without a `from_token`) so we can avoid calling
+        # `notifier.wait_for_events()`.
+        if timeout_ms == 0 or from_token is None:
+            now_token = self.event_sources.get_current_token()
+            result = await self.current_sync_for_user(
+                sync_config,
+                from_token=from_token,
+                to_token=now_token,
+            )
+        else:
+            # Otherwise, we wait for something to happen and report it to the user.
+            async def current_sync_callback(
+                before_token: StreamToken, after_token: StreamToken
+            ) -> SlidingSyncResult:
+                return await self.current_sync_for_user(
+                    sync_config,
+                    from_token=from_token,
+                    to_token=after_token,
+                )
+
+            result = await self.notifier.wait_for_events(
+                sync_config.user.to_string(),
+                timeout_ms,
+                current_sync_callback,
+                from_token=from_token,
+            )
+
+        return result
+
+    async def current_sync_for_user(
+        self,
+        sync_config: SlidingSyncConfig,
+        to_token: StreamToken,
+        from_token: Optional[StreamToken] = None,
+    ) -> SlidingSyncResult:
+        """
+        Generates the response body of a Sliding Sync result, represented as a
+        `SlidingSyncResult`.
+
+        We fetch data according to the token range (> `from_token` and <= `to_token`).
+
+        Args:
+            sync_config: Sync configuration
+            to_token: The point in the stream to sync up to.
+            from_token: The point in the stream to sync from. Token of the end of the
+                previous batch. May be `None` if this is the initial sync request.
+        """
+        user_id = sync_config.user.to_string()
+        app_service = self.store.get_app_service_by_user_id(user_id)
+        if app_service:
+            # We no longer support AS users using /sync directly.
+            # See https://github.com/matrix-org/matrix-doc/issues/1144
+            raise NotImplementedError()
+
+        # Assemble sliding window lists
+        lists: Dict[str, SlidingSyncResult.SlidingWindowList] = {}
+        if sync_config.lists:
+            # Get all of the room IDs that the user should be able to see in the sync
+            # response
+            sync_room_map = await self.get_sync_room_ids_for_user(
+                sync_config.user,
+                from_token=from_token,
+                to_token=to_token,
+            )
+
+            for list_key, list_config in sync_config.lists.items():
+                # Apply filters
+                filtered_sync_room_map = sync_room_map
+                if list_config.filters is not None:
+                    filtered_sync_room_map = await self.filter_rooms(
+                        sync_config.user, sync_room_map, list_config.filters, to_token
+                    )
+
+                sorted_room_info = await self.sort_rooms(
+                    filtered_sync_room_map, to_token
+                )
+
+                ops: List[SlidingSyncResult.SlidingWindowList.Operation] = []
+                if list_config.ranges:
+                    for range in list_config.ranges:
+                        ops.append(
+                            SlidingSyncResult.SlidingWindowList.Operation(
+                                op=OperationType.SYNC,
+                                range=range,
+                                room_ids=[
+                                    room_id
+                                    for room_id, _ in sorted_room_info[
+                                        range[0] : range[1]
+                                    ]
+                                ],
+                            )
+                        )
+
+                lists[list_key] = SlidingSyncResult.SlidingWindowList(
+                    count=len(sorted_room_info),
+                    ops=ops,
+                )
+
+        return SlidingSyncResult(
+            next_pos=to_token,
+            lists=lists,
+            # TODO: Gather room data for rooms in lists and `sync_config.room_subscriptions`
+            rooms={},
+            extensions={},
+        )
+
+    async def get_sync_room_ids_for_user(
+        self,
+        user: UserID,
+        to_token: StreamToken,
+        from_token: Optional[StreamToken] = None,
+    ) -> Dict[str, RoomsForUser]:
+        """
+        Fetch room IDs that should be listed for this user in the sync response (the
+        full room list that will be filtered, sorted, and sliced).
+
+        We're looking for rooms where the user has the following state in the token
+        range (> `from_token` and <= `to_token`):
+
+        - `invite`, `join`, `knock`, `ban` membership events
+        - Kicks (`leave` membership events where `sender` is different from the
+          `user_id`/`state_key`)
+        - `newly_left` (rooms that were left during the given token range)
+        - In order for bans/kicks to not show up in sync, you need to `/forget` those
+          rooms. This doesn't modify the event itself though and only adds the
+          `forgotten` flag to the `room_memberships` table in Synapse. There isn't a way
+          to tell when a room was forgotten at the moment so we can't factor it into the
+          from/to range.
+
+        Args:
+            user: User to fetch rooms for
+            to_token: The token to fetch rooms up to.
+            from_token: The point in the stream to sync from.
+
+        Returns:
+            A dictionary of room IDs that should be listed in the sync response along
+            with membership information in that room at the time of `to_token`.
+        """
+        user_id = user.to_string()
+
+        # First grab a current snapshot rooms for the user
+        # (also handles forgotten rooms)
+        room_for_user_list = await self.store.get_rooms_for_local_user_where_membership_is(
+            user_id=user_id,
+            # We want to fetch any kind of membership (joined and left rooms) in order
+            # to get the `event_pos` of the latest room membership event for the
+            # user.
+            #
+            # We will filter out the rooms that don't belong below (see
+            # `filter_membership_for_sync`)
+            membership_list=Membership.LIST,
+            excluded_rooms=self.rooms_to_exclude_globally,
+        )
+
+        # If the user has never joined any rooms before, we can just return an empty list
+        if not room_for_user_list:
+            return {}
+
+        # Our working list of rooms that can show up in the sync response
+        sync_room_id_set = {
+            room_for_user.room_id: room_for_user
+            for room_for_user in room_for_user_list
+            if filter_membership_for_sync(
+                membership=room_for_user.membership,
+                user_id=user_id,
+                sender=room_for_user.sender,
+            )
+        }
+
+        # Get the `RoomStreamToken` that represents the spot we queried up to when we got
+        # our membership snapshot from `get_rooms_for_local_user_where_membership_is()`.
+        #
+        # First, we need to get the max stream_ordering of each event persister instance
+        # that we queried events from.
+        instance_to_max_stream_ordering_map: Dict[str, int] = {}
+        for room_for_user in room_for_user_list:
+            instance_name = room_for_user.event_pos.instance_name
+            stream_ordering = room_for_user.event_pos.stream
+
+            current_instance_max_stream_ordering = (
+                instance_to_max_stream_ordering_map.get(instance_name)
+            )
+            if (
+                current_instance_max_stream_ordering is None
+                or stream_ordering > current_instance_max_stream_ordering
+            ):
+                instance_to_max_stream_ordering_map[instance_name] = stream_ordering
+
+        # Then assemble the `RoomStreamToken`
+        membership_snapshot_token = RoomStreamToken(
+            # Minimum position in the `instance_map`
+            stream=min(instance_to_max_stream_ordering_map.values()),
+            instance_map=immutabledict(instance_to_max_stream_ordering_map),
+        )
+
+        # Since we fetched the users room list at some point in time after the from/to
+        # tokens, we need to revert/rewind some membership changes to match the point in
+        # time of the `to_token`. In particular, we need to make these fixups:
+        #
+        # - 1a) Remove rooms that the user joined after the `to_token`
+        # - 1b) Add back rooms that the user left after the `to_token`
+        # - 2) Add back newly_left rooms (> `from_token` and <= `to_token`)
+        #
+        # Below, we're doing two separate lookups for membership changes. We could
+        # request everything for both fixups in one range, [`from_token.room_key`,
+        # `membership_snapshot_token`), but we want to avoid raw `stream_ordering`
+        # comparison without `instance_name` (which is flawed). We could refactor
+        # `event.internal_metadata` to include `instance_name` but it might turn out a
+        # little difficult and a bigger, broader Synapse change than we want to make.
+
+        # 1) -----------------------------------------------------
+
+        # 1) Fetch membership changes that fall in the range from `to_token` up to
+        # `membership_snapshot_token`
+        #
+        # If our `to_token` is already the same or ahead of the latest room membership
+        # for the user, we don't need to do any "2)" fix-ups and can just straight-up
+        # use the room list from the snapshot as a base (nothing has changed)
+        membership_change_events_after_to_token = []
+        if not membership_snapshot_token.is_before_or_eq(to_token.room_key):
+            membership_change_events_after_to_token = (
+                await self.store.get_membership_changes_for_user(
+                    user_id,
+                    from_key=to_token.room_key,
+                    to_key=membership_snapshot_token,
+                    excluded_rooms=self.rooms_to_exclude_globally,
+                )
+            )
+
+        # 1) Assemble a list of the last membership events in some given ranges. Someone
+        # could have left and joined multiple times during the given range but we only
+        # care about end-result so we grab the last one.
+        last_membership_change_by_room_id_after_to_token: Dict[str, EventBase] = {}
+        # We also need the first membership event after the `to_token` so we can step
+        # backward to the previous membership that would apply to the from/to range.
+        first_membership_change_by_room_id_after_to_token: Dict[str, EventBase] = {}
+        for event in membership_change_events_after_to_token:
+            last_membership_change_by_room_id_after_to_token[event.room_id] = event
+            # Only set if we haven't already set it
+            first_membership_change_by_room_id_after_to_token.setdefault(
+                event.room_id, event
+            )
+
+        # 1) Fixup
+        for (
+            last_membership_change_after_to_token
+        ) in last_membership_change_by_room_id_after_to_token.values():
+            room_id = last_membership_change_after_to_token.room_id
+
+            # We want to find the first membership change after the `to_token` then step
+            # backward to know the membership in the from/to range.
+            first_membership_change_after_to_token = (
+                first_membership_change_by_room_id_after_to_token.get(room_id)
+            )
+            assert first_membership_change_after_to_token is not None, (
+                "If there was a `last_membership_change_after_to_token` that we're iterating over, "
+                + "then there should be corresponding a first change. For example, even if there "
+                + "is only one event after the `to_token`, the first and last event will be same event. "
+                + "This is probably a mistake in assembling the `last_membership_change_by_room_id_after_to_token`"
+                + "/`first_membership_change_by_room_id_after_to_token` dicts above."
+            )
+            # TODO: Instead of reading from `unsigned`, refactor this to use the
+            # `current_state_delta_stream` table in the future. Probably a new
+            # `get_membership_changes_for_user()` function that uses
+            # `current_state_delta_stream` with a join to `room_memberships`. This would
+            # help in state reset scenarios since `prev_content` is looking at the
+            # current branch vs the current room state. This is all just data given to
+            # the client so no real harm to data integrity, but we'd like to be nice to
+            # the client. Since the `current_state_delta_stream` table is new, it
+            # doesn't have all events in it. Since this is Sliding Sync, if we ever need
+            # to, we can signal the client to throw all of their state away by sending
+            # "operation: RESET".
+            prev_content = first_membership_change_after_to_token.unsigned.get(
+                "prev_content", {}
+            )
+            prev_membership = prev_content.get("membership", None)
+            prev_sender = first_membership_change_after_to_token.unsigned.get(
+                "prev_sender", None
+            )
+
+            # Check if the previous membership (membership that applies to the from/to
+            # range) should be included in our `sync_room_id_set`
+            should_prev_membership_be_included = (
+                prev_membership is not None
+                and prev_sender is not None
+                and filter_membership_for_sync(
+                    membership=prev_membership,
+                    user_id=user_id,
+                    sender=prev_sender,
+                )
+            )
+
+            # Check if the last membership (membership that applies to our snapshot) was
+            # already included in our `sync_room_id_set`
+            was_last_membership_already_included = filter_membership_for_sync(
+                membership=last_membership_change_after_to_token.membership,
+                user_id=user_id,
+                sender=last_membership_change_after_to_token.sender,
+            )
+
+            # 1a) Add back rooms that the user left after the `to_token`
+            #
+            # For example, if the last membership event after the `to_token` is a leave
+            # event, then the room was excluded from `sync_room_id_set` when we first
+            # crafted it above. We should add these rooms back as long as the user also
+            # was part of the room before the `to_token`.
+            if (
+                not was_last_membership_already_included
+                and should_prev_membership_be_included
+            ):
+                sync_room_id_set[room_id] = convert_event_to_rooms_for_user(
+                    last_membership_change_after_to_token
+                )
+            # 1b) Remove rooms that the user joined (hasn't left) after the `to_token`
+            #
+            # For example, if the last membership event after the `to_token` is a "join"
+            # event, then the room was included `sync_room_id_set` when we first crafted
+            # it above. We should remove these rooms as long as the user also wasn't
+            # part of the room before the `to_token`.
+            elif (
+                was_last_membership_already_included
+                and not should_prev_membership_be_included
+            ):
+                del sync_room_id_set[room_id]
+
+        # 2) -----------------------------------------------------
+        # We fix-up newly_left rooms after the first fixup because it may have removed
+        # some left rooms that we can figure out our newly_left in the following code
+
+        # 2) Fetch membership changes that fall in the range from `from_token` up to `to_token`
+        membership_change_events_in_from_to_range = []
+        if from_token:
+            membership_change_events_in_from_to_range = (
+                await self.store.get_membership_changes_for_user(
+                    user_id,
+                    from_key=from_token.room_key,
+                    to_key=to_token.room_key,
+                    excluded_rooms=self.rooms_to_exclude_globally,
+                )
+            )
+
+        # 2) Assemble a list of the last membership events in some given ranges. Someone
+        # could have left and joined multiple times during the given range but we only
+        # care about end-result so we grab the last one.
+        last_membership_change_by_room_id_in_from_to_range: Dict[str, EventBase] = {}
+        for event in membership_change_events_in_from_to_range:
+            last_membership_change_by_room_id_in_from_to_range[event.room_id] = event
+
+        # 2) Fixup
+        for (
+            last_membership_change_in_from_to_range
+        ) in last_membership_change_by_room_id_in_from_to_range.values():
+            room_id = last_membership_change_in_from_to_range.room_id
+
+            # 2) Add back newly_left rooms (> `from_token` and <= `to_token`). We
+            # include newly_left rooms because the last event that the user should see
+            # is their own leave event
+            if last_membership_change_in_from_to_range.membership == Membership.LEAVE:
+                sync_room_id_set[room_id] = convert_event_to_rooms_for_user(
+                    last_membership_change_in_from_to_range
+                )
+
+        return sync_room_id_set
+
+    async def filter_rooms(
+        self,
+        user: UserID,
+        sync_room_map: Dict[str, RoomsForUser],
+        filters: SlidingSyncConfig.SlidingSyncList.Filters,
+        to_token: StreamToken,
+    ) -> Dict[str, RoomsForUser]:
+        """
+        Filter rooms based on the sync request.
+
+        Args:
+            user: User to filter rooms for
+            sync_room_map: Dictionary of room IDs to sort along with membership
+                information in the room at the time of `to_token`.
+            filters: Filters to apply
+            to_token: We filter based on the state of the room at this token
+
+        Returns:
+            A filtered dictionary of room IDs along with membership information in the
+            room at the time of `to_token`.
+        """
+        user_id = user.to_string()
+
+        # TODO: Apply filters
+        #
+        # TODO: Exclude partially stated rooms unless the `required_state` has
+        # `["m.room.member", "$LAZY"]`
+
+        filtered_room_id_set = set(sync_room_map.keys())
+
+        # Filter for Direct-Message (DM) rooms
+        if filters.is_dm is not None:
+            # We're using global account data (`m.direct`) instead of checking for
+            # `is_direct` on membership events because that property only appears for
+            # the invitee membership event (doesn't show up for the inviter). Account
+            # data is set by the client so it needs to be scrutinized.
+            #
+            # We're unable to take `to_token` into account for global account data since
+            # we only keep track of the latest account data for the user.
+            dm_map = await self.store.get_global_account_data_by_type_for_user(
+                user_id, AccountDataTypes.DIRECT
+            )
+
+            # Flatten out the map
+            dm_room_id_set = set()
+            if dm_map:
+                for room_ids in dm_map.values():
+                    # Account data should be a list of room IDs. Ignore anything else
+                    if isinstance(room_ids, list):
+                        for room_id in room_ids:
+                            if isinstance(room_id, str):
+                                dm_room_id_set.add(room_id)
+
+            if filters.is_dm:
+                # Only DM rooms please
+                filtered_room_id_set = filtered_room_id_set.intersection(dm_room_id_set)
+            else:
+                # Only non-DM rooms please
+                filtered_room_id_set = filtered_room_id_set.difference(dm_room_id_set)
+
+        if filters.spaces:
+            raise NotImplementedError()
+
+        # Filter for encrypted rooms
+        if filters.is_encrypted is not None:
+            # Make a copy so we don't run into an error: `Set changed size during
+            # iteration`, when we filter out and remove items
+            for room_id in list(filtered_room_id_set):
+                state_at_to_token = await self.storage_controllers.state.get_state_at(
+                    room_id,
+                    to_token,
+                    state_filter=StateFilter.from_types(
+                        [(EventTypes.RoomEncryption, "")]
+                    ),
+                )
+                is_encrypted = state_at_to_token.get((EventTypes.RoomEncryption, ""))
+
+                # If we're looking for encrypted rooms, filter out rooms that are not
+                # encrypted and vice versa
+                if (filters.is_encrypted and not is_encrypted) or (
+                    not filters.is_encrypted and is_encrypted
+                ):
+                    filtered_room_id_set.remove(room_id)
+
+        if filters.is_invite:
+            raise NotImplementedError()
+
+        if filters.room_types:
+            raise NotImplementedError()
+
+        if filters.not_room_types:
+            raise NotImplementedError()
+
+        if filters.room_name_like:
+            raise NotImplementedError()
+
+        if filters.tags:
+            raise NotImplementedError()
+
+        if filters.not_tags:
+            raise NotImplementedError()
+
+        # Assemble a new sync room map but only with the `filtered_room_id_set`
+        return {room_id: sync_room_map[room_id] for room_id in filtered_room_id_set}
+
+    async def sort_rooms(
+        self,
+        sync_room_map: Dict[str, RoomsForUser],
+        to_token: StreamToken,
+    ) -> List[Tuple[str, RoomsForUser]]:
+        """
+        Sort by `stream_ordering` of the last event that the user should see in the
+        room. `stream_ordering` is unique so we get a stable sort.
+
+        Args:
+            sync_room_map: Dictionary of room IDs to sort along with membership
+                information in the room at the time of `to_token`.
+            to_token: We sort based on the events in the room at this token (<= `to_token`)
+
+        Returns:
+            A sorted list of room IDs by `stream_ordering` along with membership information.
+        """
+
+        # Assemble a map of room ID to the `stream_ordering` of the last activity that the
+        # user should see in the room (<= `to_token`)
+        last_activity_in_room_map: Dict[str, int] = {}
+        for room_id, room_for_user in sync_room_map.items():
+            # If they are fully-joined to the room, let's find the latest activity
+            # at/before the `to_token`.
+            if room_for_user.membership == Membership.JOIN:
+                last_event_result = (
+                    await self.store.get_last_event_pos_in_room_before_stream_ordering(
+                        room_id, to_token.room_key
+                    )
+                )
+
+                # If the room has no events at/before the `to_token`, this is probably a
+                # mistake in the code that generates the `sync_room_map` since that should
+                # only give us rooms that the user had membership in during the token range.
+                assert last_event_result is not None
+
+                _, event_pos = last_event_result
+
+                last_activity_in_room_map[room_id] = event_pos.stream
+            else:
+                # Otherwise, if the user has left/been invited/knocked/been banned from
+                # a room, they shouldn't see anything past that point.
+                last_activity_in_room_map[room_id] = room_for_user.event_pos.stream
+
+        return sorted(
+            sync_room_map.items(),
+            # Sort by the last activity (stream_ordering) in the room
+            key=lambda room_info: last_activity_in_room_map[room_info[0]],
+            # We want descending order
+            reverse=True,
+        )
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 6389c51b1c..e2563428d2 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -844,7 +844,6 @@ class SyncHandler:
                     sync_config.user.to_string(),
                     recents,
                     always_include_ids=current_state_ids,
-                    msc4115_membership_on_events=self.hs_config.experimental.msc4115_membership_on_events,
                 )
                 log_kv({"recents_after_visibility_filtering": len(recents)})
             else:
@@ -930,7 +929,6 @@ class SyncHandler:
                     sync_config.user.to_string(),
                     loaded_recents,
                     always_include_ids=current_state_ids,
-                    msc4115_membership_on_events=self.hs_config.experimental.msc4115_membership_on_events,
                 )
 
                 loaded_recents = []
@@ -981,89 +979,6 @@ class SyncHandler:
             bundled_aggregations=bundled_aggregations,
         )
 
-    async def get_state_after_event(
-        self,
-        event_id: str,
-        state_filter: Optional[StateFilter] = None,
-        await_full_state: bool = True,
-    ) -> StateMap[str]:
-        """
-        Get the room state after the given event
-
-        Args:
-            event_id: event of interest
-            state_filter: The state filter used to fetch state from the database.
-            await_full_state: if `True`, will block if we do not yet have complete state
-                at the event and `state_filter` is not satisfied by partial state.
-                Defaults to `True`.
-        """
-        state_ids = await self._state_storage_controller.get_state_ids_for_event(
-            event_id,
-            state_filter=state_filter or StateFilter.all(),
-            await_full_state=await_full_state,
-        )
-
-        # using get_metadata_for_events here (instead of get_event) sidesteps an issue
-        # with redactions: if `event_id` is a redaction event, and we don't have the
-        # original (possibly because it got purged), get_event will refuse to return
-        # the redaction event, which isn't terribly helpful here.
-        #
-        # (To be fair, in that case we could assume it's *not* a state event, and
-        # therefore we don't need to worry about it. But still, it seems cleaner just
-        # to pull the metadata.)
-        m = (await self.store.get_metadata_for_events([event_id]))[event_id]
-        if m.state_key is not None and m.rejection_reason is None:
-            state_ids = dict(state_ids)
-            state_ids[(m.event_type, m.state_key)] = event_id
-
-        return state_ids
-
-    async def get_state_at(
-        self,
-        room_id: str,
-        stream_position: StreamToken,
-        state_filter: Optional[StateFilter] = None,
-        await_full_state: bool = True,
-    ) -> StateMap[str]:
-        """Get the room state at a particular stream position
-
-        Args:
-            room_id: room for which to get state
-            stream_position: point at which to get state
-            state_filter: The state filter used to fetch state from the database.
-            await_full_state: if `True`, will block if we do not yet have complete state
-                at the last event in the room before `stream_position` and
-                `state_filter` is not satisfied by partial state. Defaults to `True`.
-        """
-        # FIXME: This gets the state at the latest event before the stream ordering,
-        # which might not be the same as the "current state" of the room at the time
-        # of the stream token if there were multiple forward extremities at the time.
-        last_event_id = await self.store.get_last_event_in_room_before_stream_ordering(
-            room_id,
-            end_token=stream_position.room_key,
-        )
-
-        if last_event_id:
-            state = await self.get_state_after_event(
-                last_event_id,
-                state_filter=state_filter or StateFilter.all(),
-                await_full_state=await_full_state,
-            )
-
-        else:
-            # no events in this room - so presumably no state
-            state = {}
-
-            # (erikj) This should be rarely hit, but we've had some reports that
-            # we get more state down gappy syncs than we should, so let's add
-            # some logging.
-            logger.info(
-                "Failed to find any events in room %s at %s",
-                room_id,
-                stream_position.room_key,
-            )
-        return state
-
     async def compute_summary(
         self,
         room_id: str,
@@ -1437,7 +1352,7 @@ class SyncHandler:
             await_full_state = True
             lazy_load_members = False
 
-        state_at_timeline_end = await self.get_state_at(
+        state_at_timeline_end = await self._state_storage_controller.get_state_at(
             room_id,
             stream_position=end_token,
             state_filter=state_filter,
@@ -1521,7 +1436,7 @@ class SyncHandler:
             # We need to make sure the first event in our batch points to the
             # last event in the previous batch.
             last_event_id_prev_batch = (
-                await self.store.get_last_event_in_room_before_stream_ordering(
+                await self.store.get_last_event_id_in_room_before_stream_ordering(
                     room_id,
                     end_token=since_token.room_key,
                 )
@@ -1565,7 +1480,7 @@ class SyncHandler:
         else:
             # We can get here if the user has ignored the senders of all
             # the recent events.
-            state_at_timeline_start = await self.get_state_at(
+            state_at_timeline_start = await self._state_storage_controller.get_state_at(
                 room_id,
                 stream_position=end_token,
                 state_filter=state_filter,
@@ -1587,14 +1502,14 @@ class SyncHandler:
             # about them).
             state_filter = StateFilter.all()
 
-        state_at_previous_sync = await self.get_state_at(
+        state_at_previous_sync = await self._state_storage_controller.get_state_at(
             room_id,
             stream_position=since_token,
             state_filter=state_filter,
             await_full_state=await_full_state,
         )
 
-        state_at_timeline_end = await self.get_state_at(
+        state_at_timeline_end = await self._state_storage_controller.get_state_at(
             room_id,
             stream_position=end_token,
             state_filter=state_filter,
@@ -2002,7 +1917,7 @@ class SyncHandler:
         """
         user_id = sync_config.user.to_string()
 
-        # Note: we get the users room list *before* we get the current token, this
+        # Note: we get the users room list *before* we get the `now_token`, this
         # avoids checking back in history if rooms are joined after the token is fetched.
         token_before_rooms = self.event_sources.get_current_token()
         mutable_joined_room_ids = set(await self.store.get_rooms_for_user(user_id))
@@ -2014,10 +1929,10 @@ class SyncHandler:
         now_token = self.event_sources.get_current_token()
         log_kv({"now_token": now_token})
 
-        # Since we fetched the users room list before the token, there's a small window
-        # during which membership events may have been persisted, so we fetch these now
-        # and modify the joined room list for any changes between the get_rooms_for_user
-        # call and the get_current_token call.
+        # Since we fetched the users room list before calculating the `now_token` (see
+        # above), there's a small window during which membership events may have been
+        # persisted, so we fetch these now and modify the joined room list for any
+        # changes between the get_rooms_for_user call and the get_current_token call.
         membership_change_events = []
         if since_token:
             membership_change_events = await self.store.get_membership_changes_for_user(
@@ -2027,16 +1942,19 @@ class SyncHandler:
                 self.rooms_to_exclude_globally,
             )
 
-            mem_last_change_by_room_id: Dict[str, EventBase] = {}
+            last_membership_change_by_room_id: Dict[str, EventBase] = {}
             for event in membership_change_events:
-                mem_last_change_by_room_id[event.room_id] = event
+                last_membership_change_by_room_id[event.room_id] = event
 
             # For the latest membership event in each room found, add/remove the room ID
             # from the joined room list accordingly. In this case we only care if the
             # latest change is JOIN.
 
-            for room_id, event in mem_last_change_by_room_id.items():
+            for room_id, event in last_membership_change_by_room_id.items():
                 assert event.internal_metadata.stream_ordering
+                # As a shortcut, skip any events that happened before we got our
+                # `get_rooms_for_user()` snapshot (any changes are already represented
+                # in that list).
                 if (
                     event.internal_metadata.stream_ordering
                     < token_before_rooms.room_key.stream
@@ -2590,7 +2508,7 @@ class SyncHandler:
                 continue
 
             if room_id in sync_result_builder.joined_room_ids or has_join:
-                old_state_ids = await self.get_state_at(
+                old_state_ids = await self._state_storage_controller.get_state_at(
                     room_id,
                     since_token,
                     state_filter=StateFilter.from_types([(EventTypes.Member, user_id)]),
@@ -2620,12 +2538,14 @@ class SyncHandler:
                     newly_left_rooms.append(room_id)
                 else:
                     if not old_state_ids:
-                        old_state_ids = await self.get_state_at(
-                            room_id,
-                            since_token,
-                            state_filter=StateFilter.from_types(
-                                [(EventTypes.Member, user_id)]
-                            ),
+                        old_state_ids = (
+                            await self._state_storage_controller.get_state_at(
+                                room_id,
+                                since_token,
+                                state_filter=StateFilter.from_types(
+                                    [(EventTypes.Member, user_id)]
+                                ),
+                            )
                         )
                         old_mem_ev_id = old_state_ids.get(
                             (EventTypes.Member, user_id), None
@@ -2830,7 +2750,7 @@ class SyncHandler:
                             continue
 
                 leave_token = now_token.copy_and_replace(
-                    StreamKeyType.ROOM, RoomStreamToken(stream=event.stream_ordering)
+                    StreamKeyType.ROOM, RoomStreamToken(stream=event.event_pos.stream)
                 )
                 room_entries.append(
                     RoomSyncResultBuilder(
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index c73a589e6c..104b803b0f 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -57,7 +57,7 @@ from twisted.internet.interfaces import IReactorTime
 from twisted.internet.task import Cooperator
 from twisted.web.client import ResponseFailed
 from twisted.web.http_headers import Headers
-from twisted.web.iweb import IAgent, IBodyProducer, IResponse
+from twisted.web.iweb import UNKNOWN_LENGTH, IAgent, IBodyProducer, IResponse
 
 import synapse.metrics
 import synapse.util.retryutils
@@ -68,6 +68,7 @@ from synapse.api.errors import (
     RequestSendFailed,
     SynapseError,
 )
+from synapse.api.ratelimiting import Ratelimiter
 from synapse.crypto.context_factory import FederationPolicyForHTTPS
 from synapse.http import QuieterFileBodyProducer
 from synapse.http.client import (
@@ -1411,9 +1412,11 @@ class MatrixFederationHttpClient:
         destination: str,
         path: str,
         output_stream: BinaryIO,
+        download_ratelimiter: Ratelimiter,
+        ip_address: str,
+        max_size: int,
         args: Optional[QueryParams] = None,
         retry_on_dns_fail: bool = True,
-        max_size: Optional[int] = None,
         ignore_backoff: bool = False,
         follow_redirects: bool = False,
     ) -> Tuple[int, Dict[bytes, List[bytes]]]:
@@ -1422,6 +1425,10 @@ class MatrixFederationHttpClient:
             destination: The remote server to send the HTTP request to.
             path: The HTTP path to GET.
             output_stream: File to write the response body to.
+            download_ratelimiter: a ratelimiter to limit remote media downloads, keyed to
+                requester IP
+            ip_address: IP address of the requester
+            max_size: maximum allowable size in bytes of the file
             args: Optional dictionary used to create the query string.
             ignore_backoff: true to ignore the historical backoff data
                 and try the request anyway.
@@ -1441,11 +1448,27 @@ class MatrixFederationHttpClient:
                 federation whitelist
             RequestSendFailed: If there were problems connecting to the
                 remote, due to e.g. DNS failures, connection timeouts etc.
+            SynapseError: If the requested file exceeds ratelimits
         """
         request = MatrixFederationRequest(
             method="GET", destination=destination, path=path, query=args
         )
 
+        # check for a minimum balance of 1MiB in ratelimiter before initiating request
+        send_req, _ = await download_ratelimiter.can_do_action(
+            requester=None, key=ip_address, n_actions=1048576, update=False
+        )
+
+        if not send_req:
+            msg = "Requested file size exceeds ratelimits"
+            logger.warning(
+                "{%s} [%s] %s",
+                request.txn_id,
+                request.destination,
+                msg,
+            )
+            raise SynapseError(HTTPStatus.TOO_MANY_REQUESTS, msg, Codes.LIMIT_EXCEEDED)
+
         response = await self._send_request(
             request,
             retry_on_dns_fail=retry_on_dns_fail,
@@ -1455,12 +1478,36 @@ class MatrixFederationHttpClient:
 
         headers = dict(response.headers.getAllRawHeaders())
 
+        expected_size = response.length
+        # if we don't get an expected length then use the max length
+        if expected_size == UNKNOWN_LENGTH:
+            expected_size = max_size
+            logger.debug(
+                f"File size unknown, assuming file is max allowable size: {max_size}"
+            )
+
+        read_body, _ = await download_ratelimiter.can_do_action(
+            requester=None,
+            key=ip_address,
+            n_actions=expected_size,
+        )
+        if not read_body:
+            msg = "Requested file size exceeds ratelimits"
+            logger.warning(
+                "{%s} [%s] %s",
+                request.txn_id,
+                request.destination,
+                msg,
+            )
+            raise SynapseError(HTTPStatus.TOO_MANY_REQUESTS, msg, Codes.LIMIT_EXCEEDED)
+
         try:
-            d = read_body_with_max_size(response, output_stream, max_size)
+            # add a byte of headroom to max size as function errs at >=
+            d = read_body_with_max_size(response, output_stream, expected_size + 1)
             d.addTimeout(self.default_timeout_seconds, self.reactor)
             length = await make_deferred_yieldable(d)
         except BodyExceededMaxSize:
-            msg = "Requested file is too large > %r bytes" % (max_size,)
+            msg = "Requested file is too large > %r bytes" % (expected_size,)
             logger.warning(
                 "{%s} [%s] %s",
                 request.txn_id,
diff --git a/synapse/media/_base.py b/synapse/media/_base.py
index 3fbed6062f..19bca94170 100644
--- a/synapse/media/_base.py
+++ b/synapse/media/_base.py
@@ -25,7 +25,16 @@ import os
 import urllib
 from abc import ABC, abstractmethod
 from types import TracebackType
-from typing import Awaitable, Dict, Generator, List, Optional, Tuple, Type
+from typing import (
+    TYPE_CHECKING,
+    Awaitable,
+    Dict,
+    Generator,
+    List,
+    Optional,
+    Tuple,
+    Type,
+)
 
 import attr
 
@@ -39,6 +48,11 @@ from synapse.http.site import SynapseRequest
 from synapse.logging.context import make_deferred_yieldable
 from synapse.util.stringutils import is_ascii
 
+if TYPE_CHECKING:
+    from synapse.media.media_storage import MultipartResponder
+    from synapse.storage.databases.main.media_repository import LocalMedia
+
+
 logger = logging.getLogger(__name__)
 
 # list all text content types that will have the charset default to UTF-8 when
@@ -260,6 +274,53 @@ def _can_encode_filename_as_token(x: str) -> bool:
     return True
 
 
+async def respond_with_multipart_responder(
+    request: SynapseRequest,
+    responder: "Optional[MultipartResponder]",
+    media_info: "LocalMedia",
+) -> None:
+    """
+    Responds via a Multipart responder for the federation media `/download` requests
+
+    Args:
+        request: the federation request to respond to
+        responder: the Multipart responder which will send the response
+        media_info: metadata about the media item
+    """
+    if not responder:
+        respond_404(request)
+        return
+
+    # If we have a responder we *must* use it as a context manager.
+    with responder:
+        if request._disconnected:
+            logger.warning(
+                "Not sending response to request %s, already disconnected.", request
+            )
+            return
+
+        logger.debug("Responding to media request with responder %s", responder)
+        if media_info.media_length is not None:
+            request.setHeader(b"Content-Length", b"%d" % (media_info.media_length,))
+        request.setHeader(
+            b"Content-Type", b"multipart/mixed; boundary=%s" % responder.boundary
+        )
+
+        try:
+            await responder.write_to_consumer(request)
+        except Exception as e:
+            # The majority of the time this will be due to the client having gone
+            # away. Unfortunately, Twisted simply throws a generic exception at us
+            # in that case.
+            logger.warning("Failed to write to consumer: %s %s", type(e), e)
+
+            # Unregister the producer, if it has one, so Twisted doesn't complain
+            if request.producer:
+                request.unregisterProducer()
+
+    finish_request(request)
+
+
 async def respond_with_responder(
     request: SynapseRequest,
     responder: "Optional[Responder]",
diff --git a/synapse/media/media_repository.py b/synapse/media/media_repository.py
index 9c29e09653..c335e518a0 100644
--- a/synapse/media/media_repository.py
+++ b/synapse/media/media_repository.py
@@ -42,6 +42,7 @@ from synapse.api.errors import (
     SynapseError,
     cs_error,
 )
+from synapse.api.ratelimiting import Ratelimiter
 from synapse.config.repository import ThumbnailRequirement
 from synapse.http.server import respond_with_json
 from synapse.http.site import SynapseRequest
@@ -53,10 +54,11 @@ from synapse.media._base import (
     ThumbnailInfo,
     get_filename_from_headers,
     respond_404,
+    respond_with_multipart_responder,
     respond_with_responder,
 )
 from synapse.media.filepath import MediaFilePaths
-from synapse.media.media_storage import MediaStorage
+from synapse.media.media_storage import MediaStorage, MultipartResponder
 from synapse.media.storage_provider import StorageProviderWrapper
 from synapse.media.thumbnailer import Thumbnailer, ThumbnailError
 from synapse.media.url_previewer import UrlPreviewer
@@ -111,6 +113,12 @@ class MediaRepository:
         )
         self.prevent_media_downloads_from = hs.config.media.prevent_media_downloads_from
 
+        self.download_ratelimiter = Ratelimiter(
+            store=hs.get_storage_controllers().main,
+            clock=hs.get_clock(),
+            cfg=hs.config.ratelimiting.remote_media_downloads,
+        )
+
         # List of StorageProviders where we should search for media and
         # potentially upload to.
         storage_providers = []
@@ -422,6 +430,7 @@ class MediaRepository:
         media_id: str,
         name: Optional[str],
         max_timeout_ms: int,
+        federation: bool = False,
     ) -> None:
         """Responds to requests for local media, if exists, or returns 404.
 
@@ -433,6 +442,7 @@ class MediaRepository:
                 the filename in the Content-Disposition header of the response.
             max_timeout_ms: the maximum number of milliseconds to wait for the
                 media to be uploaded.
+            federation: whether the local media being fetched is for a federation request
 
         Returns:
             Resolves once a response has successfully been written to request
@@ -452,10 +462,17 @@ class MediaRepository:
 
         file_info = FileInfo(None, media_id, url_cache=bool(url_cache))
 
-        responder = await self.media_storage.fetch_media(file_info)
-        await respond_with_responder(
-            request, responder, media_type, media_length, upload_name
+        responder = await self.media_storage.fetch_media(
+            file_info, media_info, federation
         )
+        if federation:
+            # this really should be a Multipart responder but just in case
+            assert isinstance(responder, MultipartResponder)
+            await respond_with_multipart_responder(request, responder, media_info)
+        else:
+            await respond_with_responder(
+                request, responder, media_type, media_length, upload_name
+            )
 
     async def get_remote_media(
         self,
@@ -464,6 +481,7 @@ class MediaRepository:
         media_id: str,
         name: Optional[str],
         max_timeout_ms: int,
+        ip_address: str,
     ) -> None:
         """Respond to requests for remote media.
 
@@ -475,6 +493,7 @@ class MediaRepository:
                 the filename in the Content-Disposition header of the response.
             max_timeout_ms: the maximum number of milliseconds to wait for the
                 media to be uploaded.
+            ip_address: the IP address of the requester
 
         Returns:
             Resolves once a response has successfully been written to request
@@ -500,7 +519,11 @@ class MediaRepository:
         key = (server_name, media_id)
         async with self.remote_media_linearizer.queue(key):
             responder, media_info = await self._get_remote_media_impl(
-                server_name, media_id, max_timeout_ms
+                server_name,
+                media_id,
+                max_timeout_ms,
+                self.download_ratelimiter,
+                ip_address,
             )
 
         # We deliberately stream the file outside the lock
@@ -517,7 +540,7 @@ class MediaRepository:
             respond_404(request)
 
     async def get_remote_media_info(
-        self, server_name: str, media_id: str, max_timeout_ms: int
+        self, server_name: str, media_id: str, max_timeout_ms: int, ip_address: str
     ) -> RemoteMedia:
         """Gets the media info associated with the remote file, downloading
         if necessary.
@@ -527,6 +550,7 @@ class MediaRepository:
             media_id: The media ID of the content (as defined by the remote server).
             max_timeout_ms: the maximum number of milliseconds to wait for the
                 media to be uploaded.
+            ip_address: IP address of the requester
 
         Returns:
             The media info of the file
@@ -542,7 +566,11 @@ class MediaRepository:
         key = (server_name, media_id)
         async with self.remote_media_linearizer.queue(key):
             responder, media_info = await self._get_remote_media_impl(
-                server_name, media_id, max_timeout_ms
+                server_name,
+                media_id,
+                max_timeout_ms,
+                self.download_ratelimiter,
+                ip_address,
             )
 
         # Ensure we actually use the responder so that it releases resources
@@ -553,7 +581,12 @@ class MediaRepository:
         return media_info
 
     async def _get_remote_media_impl(
-        self, server_name: str, media_id: str, max_timeout_ms: int
+        self,
+        server_name: str,
+        media_id: str,
+        max_timeout_ms: int,
+        download_ratelimiter: Ratelimiter,
+        ip_address: str,
     ) -> Tuple[Optional[Responder], RemoteMedia]:
         """Looks for media in local cache, if not there then attempt to
         download from remote server.
@@ -564,6 +597,9 @@ class MediaRepository:
                 remote server).
             max_timeout_ms: the maximum number of milliseconds to wait for the
                 media to be uploaded.
+            download_ratelimiter: a ratelimiter limiting remote media downloads, keyed to
+                requester IP.
+            ip_address: the IP address of the requester
 
         Returns:
             A tuple of responder and the media info of the file.
@@ -596,7 +632,7 @@ class MediaRepository:
 
         try:
             media_info = await self._download_remote_file(
-                server_name, media_id, max_timeout_ms
+                server_name, media_id, max_timeout_ms, download_ratelimiter, ip_address
             )
         except SynapseError:
             raise
@@ -630,6 +666,8 @@ class MediaRepository:
         server_name: str,
         media_id: str,
         max_timeout_ms: int,
+        download_ratelimiter: Ratelimiter,
+        ip_address: str,
     ) -> RemoteMedia:
         """Attempt to download the remote file from the given server name,
         using the given file_id as the local id.
@@ -641,6 +679,9 @@ class MediaRepository:
                 locally generated.
             max_timeout_ms: the maximum number of milliseconds to wait for the
                 media to be uploaded.
+            download_ratelimiter: a ratelimiter limiting remote media downloads, keyed to
+                requester IP
+            ip_address: the IP address of the requester
 
         Returns:
             The media info of the file.
@@ -658,6 +699,8 @@ class MediaRepository:
                     output_stream=f,
                     max_size=self.max_upload_size,
                     max_timeout_ms=max_timeout_ms,
+                    download_ratelimiter=download_ratelimiter,
+                    ip_address=ip_address,
                 )
             except RequestSendFailed as e:
                 logger.warning(
diff --git a/synapse/media/media_storage.py b/synapse/media/media_storage.py
index b3cd3fd8f4..2f55d12b6b 100644
--- a/synapse/media/media_storage.py
+++ b/synapse/media/media_storage.py
@@ -19,9 +19,12 @@
 #
 #
 import contextlib
+import json
 import logging
 import os
 import shutil
+from contextlib import closing
+from io import BytesIO
 from types import TracebackType
 from typing import (
     IO,
@@ -30,14 +33,19 @@ from typing import (
     AsyncIterator,
     BinaryIO,
     Callable,
+    List,
     Optional,
     Sequence,
     Tuple,
     Type,
+    Union,
 )
+from uuid import uuid4
 
 import attr
+from zope.interface import implementer
 
+from twisted.internet import defer, interfaces
 from twisted.internet.defer import Deferred
 from twisted.internet.interfaces import IConsumer
 from twisted.protocols.basic import FileSender
@@ -48,15 +56,19 @@ from synapse.logging.opentracing import start_active_span, trace, trace_with_opn
 from synapse.util import Clock
 from synapse.util.file_consumer import BackgroundFileConsumer
 
+from ..storage.databases.main.media_repository import LocalMedia
+from ..types import JsonDict
 from ._base import FileInfo, Responder
 from .filepath import MediaFilePaths
 
 if TYPE_CHECKING:
-    from synapse.media.storage_provider import StorageProvider
+    from synapse.media.storage_provider import StorageProviderWrapper
     from synapse.server import HomeServer
 
 logger = logging.getLogger(__name__)
 
+CRLF = b"\r\n"
+
 
 class MediaStorage:
     """Responsible for storing/fetching files from local sources.
@@ -73,7 +85,7 @@ class MediaStorage:
         hs: "HomeServer",
         local_media_directory: str,
         filepaths: MediaFilePaths,
-        storage_providers: Sequence["StorageProvider"],
+        storage_providers: Sequence["StorageProviderWrapper"],
     ):
         self.hs = hs
         self.reactor = hs.get_reactor()
@@ -169,15 +181,23 @@ class MediaStorage:
 
             raise e from None
 
-    async def fetch_media(self, file_info: FileInfo) -> Optional[Responder]:
+    async def fetch_media(
+        self,
+        file_info: FileInfo,
+        media_info: Optional[LocalMedia] = None,
+        federation: bool = False,
+    ) -> Optional[Responder]:
         """Attempts to fetch media described by file_info from the local cache
         and configured storage providers.
 
         Args:
-            file_info
+            file_info: Metadata about the media file
+            media_info: Metadata about the media item
+            federation: Whether this file is being fetched for a federation request
 
         Returns:
-            Returns a Responder if the file was found, otherwise None.
+            If the file was found returns a Responder (a Multipart Responder if the requested
+            file is for the federation /download endpoint), otherwise None.
         """
         paths = [self._file_info_to_path(file_info)]
 
@@ -197,12 +217,19 @@ class MediaStorage:
             local_path = os.path.join(self.local_media_directory, path)
             if os.path.exists(local_path):
                 logger.debug("responding with local file %s", local_path)
-                return FileResponder(open(local_path, "rb"))
+                if federation:
+                    assert media_info is not None
+                    boundary = uuid4().hex.encode("ascii")
+                    return MultipartResponder(
+                        open(local_path, "rb"), media_info, boundary
+                    )
+                else:
+                    return FileResponder(open(local_path, "rb"))
             logger.debug("local file %s did not exist", local_path)
 
         for provider in self.storage_providers:
             for path in paths:
-                res: Any = await provider.fetch(path, file_info)
+                res: Any = await provider.fetch(path, file_info, media_info, federation)
                 if res:
                     logger.debug("Streaming %s from %s", path, provider)
                     return res
@@ -316,7 +343,7 @@ class FileResponder(Responder):
     """Wraps an open file that can be sent to a request.
 
     Args:
-        open_file: A file like object to be streamed ot the client,
+        open_file: A file like object to be streamed to the client,
             is closed when finished streaming.
     """
 
@@ -337,6 +364,38 @@ class FileResponder(Responder):
         self.open_file.close()
 
 
+class MultipartResponder(Responder):
+    """Wraps an open file, formats the response according to MSC3916 and sends it to a
+    federation request.
+
+    Args:
+        open_file: A file like object to be streamed to the client,
+            is closed when finished streaming.
+        media_info: metadata about the media item
+        boundary: bytes to use for the multipart response boundary
+    """
+
+    def __init__(self, open_file: IO, media_info: LocalMedia, boundary: bytes) -> None:
+        self.open_file = open_file
+        self.media_info = media_info
+        self.boundary = boundary
+
+    def write_to_consumer(self, consumer: IConsumer) -> Deferred:
+        return make_deferred_yieldable(
+            MultipartFileSender().beginFileTransfer(
+                self.open_file, consumer, self.media_info.media_type, {}, self.boundary
+            )
+        )
+
+    def __exit__(
+        self,
+        exc_type: Optional[Type[BaseException]],
+        exc_val: Optional[BaseException],
+        exc_tb: Optional[TracebackType],
+    ) -> None:
+        self.open_file.close()
+
+
 class SpamMediaException(NotFoundError):
     """The media was blocked by a spam checker, so we simply 404 the request (in
     the same way as if it was quarantined).
@@ -370,3 +429,151 @@ class ReadableFileWrapper:
 
                 # We yield to the reactor by sleeping for 0 seconds.
                 await self.clock.sleep(0)
+
+
+@implementer(interfaces.IProducer)
+class MultipartFileSender:
+    """
+    A producer that sends the contents of a file to a federation request in the format
+    outlined in MSC3916 - a multipart/format-data response where the first field is a
+    JSON object and the second is the requested file.
+
+    This is a slight re-writing of twisted.protocols.basic.FileSender to achieve the format
+    outlined above.
+    """
+
+    CHUNK_SIZE = 2**14
+
+    lastSent = ""
+    deferred: Optional[defer.Deferred] = None
+
+    def beginFileTransfer(
+        self,
+        file: IO,
+        consumer: IConsumer,
+        file_content_type: str,
+        json_object: JsonDict,
+        boundary: bytes,
+    ) -> Deferred:
+        """
+        Begin transferring a file
+
+        Args:
+            file: The file object to read data from
+            consumer: The synapse request to write the data to
+            file_content_type: The content-type of the file
+            json_object: The JSON object to write to the first field of the response
+            boundary: bytes to be used as the multipart/form-data boundary
+
+        Returns:  A deferred whose callback will be invoked when the file has
+        been completely written to the consumer. The last byte written to the
+        consumer is passed to the callback.
+        """
+        self.file: Optional[IO] = file
+        self.consumer = consumer
+        self.json_field = json_object
+        self.json_field_written = False
+        self.content_type_written = False
+        self.file_content_type = file_content_type
+        self.boundary = boundary
+        self.deferred: Deferred = defer.Deferred()
+        self.consumer.registerProducer(self, False)
+        # while it's not entirely clear why this assignment is necessary, it mirrors
+        # the behavior in FileSender.beginFileTransfer and thus is preserved here
+        deferred = self.deferred
+        return deferred
+
+    def resumeProducing(self) -> None:
+        # write the first field, which will always be a json field
+        if not self.json_field_written:
+            self.consumer.write(CRLF + b"--" + self.boundary + CRLF)
+
+            content_type = Header(b"Content-Type", b"application/json")
+            self.consumer.write(bytes(content_type) + CRLF)
+
+            json_field = json.dumps(self.json_field)
+            json_bytes = json_field.encode("utf-8")
+            self.consumer.write(json_bytes)
+            self.consumer.write(CRLF + b"--" + self.boundary + CRLF)
+
+            self.json_field_written = True
+
+        chunk: Any = ""
+        if self.file:
+            # if we haven't written the content type yet, do so
+            if not self.content_type_written:
+                type = self.file_content_type.encode("utf-8")
+                content_type = Header(b"Content-Type", type)
+                self.consumer.write(bytes(content_type) + CRLF)
+                self.content_type_written = True
+
+            chunk = self.file.read(self.CHUNK_SIZE)
+
+        if not chunk:
+            # we've reached the end of the file
+            self.consumer.write(CRLF + b"--" + self.boundary + b"--" + CRLF)
+            self.file = None
+            self.consumer.unregisterProducer()
+
+            if self.deferred:
+                self.deferred.callback(self.lastSent)
+                self.deferred = None
+            return
+
+        self.consumer.write(chunk)
+        self.lastSent = chunk[-1:]
+
+    def pauseProducing(self) -> None:
+        pass
+
+    def stopProducing(self) -> None:
+        if self.deferred:
+            self.deferred.errback(Exception("Consumer asked us to stop producing"))
+            self.deferred = None
+
+
+class Header:
+    """
+    `Header` This class is a tiny wrapper that produces
+    request headers. We can't use standard python header
+    class because it encodes unicode fields using =? bla bla ?=
+    encoding, which is correct, but no one in HTTP world expects
+    that, everyone wants utf-8 raw bytes. (stolen from treq.multipart)
+
+    """
+
+    def __init__(
+        self,
+        name: bytes,
+        value: Any,
+        params: Optional[List[Tuple[Any, Any]]] = None,
+    ):
+        self.name = name
+        self.value = value
+        self.params = params or []
+
+    def add_param(self, name: Any, value: Any) -> None:
+        self.params.append((name, value))
+
+    def __bytes__(self) -> bytes:
+        with closing(BytesIO()) as h:
+            h.write(self.name + b": " + escape(self.value).encode("us-ascii"))
+            if self.params:
+                for name, val in self.params:
+                    h.write(b"; ")
+                    h.write(escape(name).encode("us-ascii"))
+                    h.write(b"=")
+                    h.write(b'"' + escape(val).encode("utf-8") + b'"')
+            h.seek(0)
+            return h.read()
+
+
+def escape(value: Union[str, bytes]) -> str:
+    """
+    This function prevents header values from corrupting the request,
+    a newline in the file name parameter makes form-data request unreadable
+    for a majority of parsers. (stolen from treq.multipart)
+    """
+    if isinstance(value, bytes):
+        value = value.decode("utf-8")
+    return value.replace("\r", "").replace("\n", "").replace('"', '\\"')
diff --git a/synapse/media/storage_provider.py b/synapse/media/storage_provider.py
index 06e5d27a53..a2d50adf65 100644
--- a/synapse/media/storage_provider.py
+++ b/synapse/media/storage_provider.py
@@ -24,14 +24,16 @@ import logging
 import os
 import shutil
 from typing import TYPE_CHECKING, Callable, Optional
+from uuid import uuid4
 
 from synapse.config._base import Config
 from synapse.logging.context import defer_to_thread, run_in_background
 from synapse.logging.opentracing import start_active_span, trace_with_opname
 from synapse.util.async_helpers import maybe_awaitable
 
+from ..storage.databases.main.media_repository import LocalMedia
 from ._base import FileInfo, Responder
-from .media_storage import FileResponder
+from .media_storage import FileResponder, MultipartResponder
 
 logger = logging.getLogger(__name__)
 
@@ -55,13 +57,21 @@ class StorageProvider(metaclass=abc.ABCMeta):
         """
 
     @abc.abstractmethod
-    async def fetch(self, path: str, file_info: FileInfo) -> Optional[Responder]:
+    async def fetch(
+        self,
+        path: str,
+        file_info: FileInfo,
+        media_info: Optional[LocalMedia] = None,
+        federation: bool = False,
+    ) -> Optional[Responder]:
         """Attempt to fetch the file described by file_info and stream it
         into writer.
 
         Args:
             path: Relative path of file in local cache
             file_info: The metadata of the file.
+            media_info: metadata of the media item
+            federation: Whether the requested media is for a federation request
 
         Returns:
             Returns a Responder if the provider has the file, otherwise returns None.
@@ -124,7 +134,13 @@ class StorageProviderWrapper(StorageProvider):
             run_in_background(store)
 
     @trace_with_opname("StorageProviderWrapper.fetch")
-    async def fetch(self, path: str, file_info: FileInfo) -> Optional[Responder]:
+    async def fetch(
+        self,
+        path: str,
+        file_info: FileInfo,
+        media_info: Optional[LocalMedia] = None,
+        federation: bool = False,
+    ) -> Optional[Responder]:
         if file_info.url_cache:
             # Files in the URL preview cache definitely aren't stored here,
             # so avoid any potentially slow I/O or network access.
@@ -132,7 +148,9 @@ class StorageProviderWrapper(StorageProvider):
 
         # store_file is supposed to return an Awaitable, but guard
         # against improper implementations.
-        return await maybe_awaitable(self.backend.fetch(path, file_info))
+        return await maybe_awaitable(
+            self.backend.fetch(path, file_info, media_info, federation)
+        )
 
 
 class FileStorageProviderBackend(StorageProvider):
@@ -172,11 +190,23 @@ class FileStorageProviderBackend(StorageProvider):
             )
 
     @trace_with_opname("FileStorageProviderBackend.fetch")
-    async def fetch(self, path: str, file_info: FileInfo) -> Optional[Responder]:
+    async def fetch(
+        self,
+        path: str,
+        file_info: FileInfo,
+        media_info: Optional[LocalMedia] = None,
+        federation: bool = False,
+    ) -> Optional[Responder]:
         """See StorageProvider.fetch"""
 
         backup_fname = os.path.join(self.base_directory, path)
         if os.path.isfile(backup_fname):
+            if federation:
+                assert media_info is not None
+                boundary = uuid4().hex.encode("ascii")
+                return MultipartResponder(
+                    open(backup_fname, "rb"), media_info, boundary
+                )
             return FileResponder(open(backup_fname, "rb"))
 
         return None
diff --git a/synapse/media/thumbnailer.py b/synapse/media/thumbnailer.py
index cc3acf51e1..f8a9560784 100644
--- a/synapse/media/thumbnailer.py
+++ b/synapse/media/thumbnailer.py
@@ -359,9 +359,10 @@ class ThumbnailProvider:
         desired_method: str,
         desired_type: str,
         max_timeout_ms: int,
+        ip_address: str,
     ) -> None:
         media_info = await self.media_repo.get_remote_media_info(
-            server_name, media_id, max_timeout_ms
+            server_name, media_id, max_timeout_ms, ip_address
         )
         if not media_info:
             respond_404(request)
@@ -422,12 +423,13 @@ class ThumbnailProvider:
         method: str,
         m_type: str,
         max_timeout_ms: int,
+        ip_address: str,
     ) -> None:
         # TODO: Don't download the whole remote file
         # We should proxy the thumbnail from the remote server instead of
         # downloading the remote file and generating our own thumbnails.
         media_info = await self.media_repo.get_remote_media_info(
-            server_name, media_id, max_timeout_ms
+            server_name, media_id, max_timeout_ms, ip_address
         )
         if not media_info:
             return
diff --git a/synapse/notifier.py b/synapse/notifier.py
index ced9e9ad66..c87eb748c0 100644
--- a/synapse/notifier.py
+++ b/synapse/notifier.py
@@ -721,7 +721,6 @@ class Notifier:
                         user.to_string(),
                         new_events,
                         is_peeking=is_peeking,
-                        msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
                     )
                 elif keyname == StreamKeyType.PRESENCE:
                     now = self.clock.time_msec()
diff --git a/synapse/push/mailer.py b/synapse/push/mailer.py
index 49ce9d6dda..77cc69a71f 100644
--- a/synapse/push/mailer.py
+++ b/synapse/push/mailer.py
@@ -532,7 +532,6 @@ class Mailer:
             self._storage_controllers,
             user_id,
             results.events_before,
-            msc4115_membership_on_events=self.hs.config.experimental.msc4115_membership_on_events,
         )
         the_events.append(notif_event)
 
diff --git a/synapse/rest/__init__.py b/synapse/rest/__init__.py
index 534dc0e276..0024ccf708 100644
--- a/synapse/rest/__init__.py
+++ b/synapse/rest/__init__.py
@@ -53,7 +53,7 @@ from synapse.rest.client import (
     register,
     relations,
     rendezvous,
-    report_event,
+    reporting,
     room,
     room_keys,
     room_upgrade_rest_servlet,
@@ -128,7 +128,7 @@ class ClientRestResource(JsonResource):
         tags.register_servlets(hs, client_resource)
         account_data.register_servlets(hs, client_resource)
         if is_main_process:
-            report_event.register_servlets(hs, client_resource)
+            reporting.register_servlets(hs, client_resource)
             openid.register_servlets(hs, client_resource)
         notifications.register_servlets(hs, client_resource)
         devices.register_servlets(hs, client_resource)
diff --git a/synapse/rest/admin/experimental_features.py b/synapse/rest/admin/experimental_features.py
index 52eb9e62db..c5a00c490c 100644
--- a/synapse/rest/admin/experimental_features.py
+++ b/synapse/rest/admin/experimental_features.py
@@ -41,7 +41,6 @@ class ExperimentalFeature(str, Enum):
 
     MSC3026 = "msc3026"
     MSC3881 = "msc3881"
-    MSC3967 = "msc3967"
 
 
 class ExperimentalFeaturesRestServlet(RestServlet):
diff --git a/synapse/rest/client/account.py b/synapse/rest/client/account.py
index 6ac07d354c..8daa449f9e 100644
--- a/synapse/rest/client/account.py
+++ b/synapse/rest/client/account.py
@@ -56,14 +56,14 @@ from synapse.http.servlet import (
 from synapse.http.site import SynapseRequest
 from synapse.metrics import threepid_send_requests
 from synapse.push.mailer import Mailer
-from synapse.rest.client.models import (
+from synapse.types import JsonDict
+from synapse.types.rest import RequestBodyModel
+from synapse.types.rest.client import (
     AuthenticationData,
     ClientSecretStr,
     EmailRequestTokenBody,
     MsisdnRequestTokenBody,
 )
-from synapse.rest.models import RequestBodyModel
-from synapse.types import JsonDict
 from synapse.util.msisdn import phone_number_to_msisdn
 from synapse.util.stringutils import assert_valid_client_secret, random_string
 from synapse.util.threepids import check_3pid_allowed, validate_email
diff --git a/synapse/rest/client/devices.py b/synapse/rest/client/devices.py
index b1b803549e..8313d687b7 100644
--- a/synapse/rest/client/devices.py
+++ b/synapse/rest/client/devices.py
@@ -42,9 +42,9 @@ from synapse.http.servlet import (
 )
 from synapse.http.site import SynapseRequest
 from synapse.rest.client._base import client_patterns, interactive_auth_handler
-from synapse.rest.client.models import AuthenticationData
-from synapse.rest.models import RequestBodyModel
 from synapse.types import JsonDict
+from synapse.types.rest import RequestBodyModel
+from synapse.types.rest.client import AuthenticationData
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/rest/client/directory.py b/synapse/rest/client/directory.py
index 8099fdf3e4..11fdd0f7c6 100644
--- a/synapse/rest/client/directory.py
+++ b/synapse/rest/client/directory.py
@@ -41,8 +41,8 @@ from synapse.http.servlet import (
 )
 from synapse.http.site import SynapseRequest
 from synapse.rest.client._base import client_patterns
-from synapse.rest.models import RequestBodyModel
 from synapse.types import JsonDict, RoomAlias
+from synapse.types.rest import RequestBodyModel
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
diff --git a/synapse/rest/client/keys.py b/synapse/rest/client/keys.py
index a0017257ce..67de634eab 100644
--- a/synapse/rest/client/keys.py
+++ b/synapse/rest/client/keys.py
@@ -36,7 +36,6 @@ from synapse.http.servlet import (
 )
 from synapse.http.site import SynapseRequest
 from synapse.logging.opentracing import log_kv, set_tag
-from synapse.replication.http.devices import ReplicationUploadKeysForUserRestServlet
 from synapse.rest.client._base import client_patterns, interactive_auth_handler
 from synapse.types import JsonDict, StreamToken
 from synapse.util.cancellation import cancellable
@@ -105,13 +104,8 @@ class KeyUploadServlet(RestServlet):
         self.auth = hs.get_auth()
         self.e2e_keys_handler = hs.get_e2e_keys_handler()
         self.device_handler = hs.get_device_handler()
-
-        if hs.config.worker.worker_app is None:
-            # if main process
-            self.key_uploader = self.e2e_keys_handler.upload_keys_for_user
-        else:
-            # then a worker
-            self.key_uploader = ReplicationUploadKeysForUserRestServlet.make_client(hs)
+        self._clock = hs.get_clock()
+        self._store = hs.get_datastores().main
 
     async def on_POST(
         self, request: SynapseRequest, device_id: Optional[str]
@@ -151,9 +145,10 @@ class KeyUploadServlet(RestServlet):
                 400, "To upload keys, you must pass device_id when authenticating"
             )
 
-        result = await self.key_uploader(
+        result = await self.e2e_keys_handler.upload_keys_for_user(
             user_id=user_id, device_id=device_id, keys=body
         )
+
         return 200, result
 
 
@@ -387,44 +382,35 @@ class SigningKeyUploadServlet(RestServlet):
             master_key_updatable_without_uia,
         ) = await self.e2e_keys_handler.check_cross_signing_setup(user_id)
 
-        # Before MSC3967 we required UIA both when setting up cross signing for the
-        # first time and when resetting the device signing key. With MSC3967 we only
-        # require UIA when resetting cross-signing, and not when setting up the first
-        # time. Because there is no UIA in MSC3861, for now we throw an error if the
-        # user tries to reset the device signing key when MSC3861 is enabled, but allow
-        # first-time setup.
-        if self.hs.config.experimental.msc3861.enabled:
-            # The auth service has to explicitly mark the master key as replaceable
-            # without UIA to reset the device signing key with MSC3861.
-            if is_cross_signing_setup and not master_key_updatable_without_uia:
-                config = self.hs.config.experimental.msc3861
-                if config.account_management_url is not None:
-                    url = f"{config.account_management_url}?action=org.matrix.cross_signing_reset"
-                else:
-                    url = config.issuer
-
-                raise SynapseError(
-                    HTTPStatus.NOT_IMPLEMENTED,
-                    "To reset your end-to-end encryption cross-signing identity, "
-                    f"you first need to approve it at {url} and then try again.",
-                    Codes.UNRECOGNIZED,
-                )
-            # But first-time setup is fine
-
-        elif self.hs.config.experimental.msc3967_enabled:
-            # MSC3967 allows this endpoint to 200 OK for idempotency. Resending exactly the same
-            # keys should just 200 OK without doing a UIA prompt.
-            keys_are_different = await self.e2e_keys_handler.has_different_keys(
-                user_id, body
-            )
-            if not keys_are_different:
-                # FIXME: we do not fallthrough to upload_signing_keys_for_user because confusingly
-                # if we do, we 500 as it looks like it tries to INSERT the same key twice, causing a
-                # unique key constraint violation. This sounds like a bug?
-                return 200, {}
-            # the keys are different, is x-signing set up? If no, then the keys don't exist which is
-            # why they are different. If yes, then we need to UIA to change them.
-            if is_cross_signing_setup:
+        # Resending exactly the same keys should just 200 OK without doing a UIA prompt.
+        keys_are_different = await self.e2e_keys_handler.has_different_keys(
+            user_id, body
+        )
+        if not keys_are_different:
+            return 200, {}
+
+        # The keys are different; is x-signing set up? If no, then this is first-time
+        # setup, and that is allowed without UIA, per MSC3967.
+        # If yes, then we need to authenticate the change.
+        if is_cross_signing_setup:
+            # With MSC3861, UIA is not possible. Instead, the auth service has to
+            # explicitly mark the master key as replaceable.
+            if self.hs.config.experimental.msc3861.enabled:
+                if not master_key_updatable_without_uia:
+                    config = self.hs.config.experimental.msc3861
+                    if config.account_management_url is not None:
+                        url = f"{config.account_management_url}?action=org.matrix.cross_signing_reset"
+                    else:
+                        url = config.issuer
+
+                    raise SynapseError(
+                        HTTPStatus.NOT_IMPLEMENTED,
+                        "To reset your end-to-end encryption cross-signing identity, "
+                        f"you first need to approve it at {url} and then try again.",
+                        Codes.UNRECOGNIZED,
+                    )
+            else:
+                # Without MSC3861, we require UIA.
                 await self.auth_handler.validate_user_via_ui_auth(
                     requester,
                     request,
@@ -433,18 +419,6 @@ class SigningKeyUploadServlet(RestServlet):
                     # Do not allow skipping of UIA auth.
                     can_skip_ui_auth=False,
                 )
-            # Otherwise we don't require UIA since we are setting up cross signing for first time
-        else:
-            # Previous behaviour is to always require UIA but allow it to be skipped
-            await self.auth_handler.validate_user_via_ui_auth(
-                requester,
-                request,
-                body,
-                "add a device signing key to your account",
-                # Allow skipping of UI auth since this is frequently called directly
-                # after login and it is silly to ask users to re-auth immediately.
-                can_skip_ui_auth=True,
-            )
 
         result = await self.e2e_keys_handler.upload_signing_keys_for_user(user_id, body)
         return 200, result
diff --git a/synapse/rest/client/knock.py b/synapse/rest/client/knock.py
index ff52a9bf8c..e31687fc13 100644
--- a/synapse/rest/client/knock.py
+++ b/synapse/rest/client/knock.py
@@ -53,6 +53,7 @@ class KnockRoomAliasServlet(RestServlet):
         super().__init__()
         self.room_member_handler = hs.get_room_member_handler()
         self.auth = hs.get_auth()
+        self._support_via = hs.config.experimental.msc4156_enabled
 
     async def on_POST(
         self,
@@ -74,6 +75,13 @@ class KnockRoomAliasServlet(RestServlet):
             remote_room_hosts = parse_strings_from_args(
                 args, "server_name", required=False
             )
+            if self._support_via:
+                remote_room_hosts = parse_strings_from_args(
+                    args,
+                    "org.matrix.msc4156.via",
+                    default=remote_room_hosts,
+                    required=False,
+                )
         elif RoomAlias.is_valid(room_identifier):
             handler = self.room_member_handler
             room_alias = RoomAlias.from_string(room_identifier)
diff --git a/synapse/rest/client/media.py b/synapse/rest/client/media.py
index 172d240783..0c089163c1 100644
--- a/synapse/rest/client/media.py
+++ b/synapse/rest/client/media.py
@@ -174,6 +174,7 @@ class UnstableThumbnailResource(RestServlet):
                 respond_404(request)
                 return
 
+            ip_address = request.getClientAddress().host
             remote_resp_function = (
                 self.thumbnailer.select_or_generate_remote_thumbnail
                 if self.dynamic_thumbnails
@@ -188,6 +189,7 @@ class UnstableThumbnailResource(RestServlet):
                 method,
                 m_type,
                 max_timeout_ms,
+                ip_address,
             )
             self.media_repo.mark_recently_accessed(server_name, media_id)
 
diff --git a/synapse/rest/client/models.py b/synapse/rest/client/models.py
deleted file mode 100644
index fc1aed2889..0000000000
--- a/synapse/rest/client/models.py
+++ /dev/null
@@ -1,99 +0,0 @@
-#
-# This file is licensed under the Affero General Public License (AGPL) version 3.
-#
-# Copyright 2022 The Matrix.org Foundation C.I.C.
-# Copyright (C) 2023 New Vector, Ltd
-#
-# This program is free software: you can redistribute it and/or modify
-# it under the terms of the GNU Affero General Public License as
-# published by the Free Software Foundation, either version 3 of the
-# License, or (at your option) any later version.
-#
-# See the GNU Affero General Public License for more details:
-# <https://www.gnu.org/licenses/agpl-3.0.html>.
-#
-# Originally licensed under the Apache License, Version 2.0:
-# <http://www.apache.org/licenses/LICENSE-2.0>.
-#
-# [This file includes modifications made by New Vector Limited]
-#
-#
-from typing import TYPE_CHECKING, Dict, Optional
-
-from synapse._pydantic_compat import HAS_PYDANTIC_V2
-
-if TYPE_CHECKING or HAS_PYDANTIC_V2:
-    from pydantic.v1 import Extra, StrictInt, StrictStr, constr, validator
-else:
-    from pydantic import Extra, StrictInt, StrictStr, constr, validator
-
-from synapse.rest.models import RequestBodyModel
-from synapse.util.threepids import validate_email
-
-
-class AuthenticationData(RequestBodyModel):
-    """
-    Data used during user-interactive authentication.
-
-    (The name "Authentication Data" is taken directly from the spec.)
-
-    Additional keys will be present, depending on the `type` field. Use
-    `.dict(exclude_unset=True)` to access them.
-    """
-
-    class Config:
-        extra = Extra.allow
-
-    session: Optional[StrictStr] = None
-    type: Optional[StrictStr] = None
-
-
-if TYPE_CHECKING:
-    ClientSecretStr = StrictStr
-else:
-    # See also assert_valid_client_secret()
-    ClientSecretStr = constr(
-        regex="[0-9a-zA-Z.=_-]",  # noqa: F722
-        min_length=1,
-        max_length=255,
-        strict=True,
-    )
-
-
-class ThreepidRequestTokenBody(RequestBodyModel):
-    client_secret: ClientSecretStr
-    id_server: Optional[StrictStr]
-    id_access_token: Optional[StrictStr]
-    next_link: Optional[StrictStr]
-    send_attempt: StrictInt
-
-    @validator("id_access_token", always=True)
-    def token_required_for_identity_server(
-        cls, token: Optional[str], values: Dict[str, object]
-    ) -> Optional[str]:
-        if values.get("id_server") is not None and token is None:
-            raise ValueError("id_access_token is required if an id_server is supplied.")
-        return token
-
-
-class EmailRequestTokenBody(ThreepidRequestTokenBody):
-    email: StrictStr
-
-    # Canonicalise the email address. The addresses are all stored canonicalised
-    # in the database. This allows the user to reset his password without having to
-    # know the exact spelling (eg. upper and lower case) of address in the database.
-    # Without this, an email stored in the database as "foo@bar.com" would cause
-    # user requests for "FOO@bar.com" to raise a Not Found error.
-    _email_validator = validator("email", allow_reuse=True)(validate_email)
-
-
-if TYPE_CHECKING:
-    ISO3116_1_Alpha_2 = StrictStr
-else:
-    # Per spec: two-letter uppercase ISO-3166-1-alpha-2
-    ISO3116_1_Alpha_2 = constr(regex="[A-Z]{2}", strict=True)
-
-
-class MsisdnRequestTokenBody(ThreepidRequestTokenBody):
-    country: ISO3116_1_Alpha_2
-    phone_number: StrictStr
diff --git a/synapse/rest/client/report_event.py b/synapse/rest/client/reporting.py
index 447281931e..4eee53e5a8 100644
--- a/synapse/rest/client/report_event.py
+++ b/synapse/rest/client/reporting.py
@@ -23,17 +23,28 @@ import logging
 from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
+from synapse._pydantic_compat import HAS_PYDANTIC_V2
 from synapse.api.errors import AuthError, Codes, NotFoundError, SynapseError
 from synapse.http.server import HttpServer
-from synapse.http.servlet import RestServlet, parse_json_object_from_request
+from synapse.http.servlet import (
+    RestServlet,
+    parse_and_validate_json_object_from_request,
+    parse_json_object_from_request,
+)
 from synapse.http.site import SynapseRequest
 from synapse.types import JsonDict
+from synapse.types.rest import RequestBodyModel
 
 from ._base import client_patterns
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
 
+if TYPE_CHECKING or HAS_PYDANTIC_V2:
+    from pydantic.v1 import StrictStr
+else:
+    from pydantic import StrictStr
+
 logger = logging.getLogger(__name__)
 
 
@@ -95,5 +106,57 @@ class ReportEventRestServlet(RestServlet):
         return 200, {}
 
 
+class ReportRoomRestServlet(RestServlet):
+    """This endpoint lets clients report a room for abuse.
+
+    Whilst MSC4151 is not yet merged, this unstable endpoint is enabled on matrix.org
+    for content moderation purposes, and therefore backwards compatibility should be
+    carefully considered when changing anything on this endpoint.
+
+    More details on the MSC: https://github.com/matrix-org/matrix-spec-proposals/pull/4151
+    """
+
+    PATTERNS = client_patterns(
+        "/org.matrix.msc4151/rooms/(?P<room_id>[^/]*)/report$",
+        releases=[],
+        v1=False,
+        unstable=True,
+    )
+
+    def __init__(self, hs: "HomeServer"):
+        super().__init__()
+        self.hs = hs
+        self.auth = hs.get_auth()
+        self.clock = hs.get_clock()
+        self.store = hs.get_datastores().main
+
+    class PostBody(RequestBodyModel):
+        reason: StrictStr
+
+    async def on_POST(
+        self, request: SynapseRequest, room_id: str
+    ) -> Tuple[int, JsonDict]:
+        requester = await self.auth.get_user_by_req(request)
+        user_id = requester.user.to_string()
+
+        body = parse_and_validate_json_object_from_request(request, self.PostBody)
+
+        room = await self.store.get_room(room_id)
+        if room is None:
+            raise NotFoundError("Room does not exist")
+
+        await self.store.add_room_report(
+            room_id=room_id,
+            user_id=user_id,
+            reason=body.reason,
+            received_ts=self.clock.time_msec(),
+        )
+
+        return 200, {}
+
+
 def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
     ReportEventRestServlet(hs).register(http_server)
+
+    if hs.config.experimental.msc4151_enabled:
+        ReportRoomRestServlet(hs).register(http_server)
diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index fb4d44211e..c98241f6ce 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -292,6 +292,9 @@ class RoomStateEventRestServlet(RestServlet):
         try:
             if event_type == EventTypes.Member:
                 membership = content.get("membership", None)
+                if not isinstance(membership, str):
+                    raise SynapseError(400, "Invalid membership (must be a string)")
+
                 event_id, _ = await self.room_member_handler.update_membership(
                     requester,
                     target=UserID.from_string(state_key),
@@ -414,6 +417,7 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, TransactionRestServlet):
         super().__init__(hs)
         super(ResolveRoomIdMixin, self).__init__(hs)  # ensure the Mixin is set up
         self.auth = hs.get_auth()
+        self._support_via = hs.config.experimental.msc4156_enabled
 
     def register(self, http_server: HttpServer) -> None:
         # /join/$room_identifier[/$txn_id]
@@ -432,6 +436,13 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, TransactionRestServlet):
         # twisted.web.server.Request.args is incorrectly defined as Optional[Any]
         args: Dict[bytes, List[bytes]] = request.args  # type: ignore
         remote_room_hosts = parse_strings_from_args(args, "server_name", required=False)
+        if self._support_via:
+            remote_room_hosts = parse_strings_from_args(
+                args,
+                "org.matrix.msc4156.via",
+                default=remote_room_hosts,
+                required=False,
+            )
         room_id, remote_room_hosts = await self.resolve_room_id(
             room_identifier,
             remote_room_hosts,
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index 27ea943e31..1b0ac20d94 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -33,6 +33,7 @@ from synapse.events.utils import (
     format_event_raw,
 )
 from synapse.handlers.presence import format_user_presence_state
+from synapse.handlers.sliding_sync import SlidingSyncConfig, SlidingSyncResult
 from synapse.handlers.sync import (
     ArchivedSyncResult,
     InvitedSyncResult,
@@ -43,10 +44,17 @@ from synapse.handlers.sync import (
     SyncVersion,
 )
 from synapse.http.server import HttpServer
-from synapse.http.servlet import RestServlet, parse_boolean, parse_integer, parse_string
+from synapse.http.servlet import (
+    RestServlet,
+    parse_and_validate_json_object_from_request,
+    parse_boolean,
+    parse_integer,
+    parse_string,
+)
 from synapse.http.site import SynapseRequest
 from synapse.logging.opentracing import trace_with_opname
 from synapse.types import JsonDict, Requester, StreamToken
+from synapse.types.rest.client import SlidingSyncBody
 from synapse.util import json_decoder
 from synapse.util.caches.lrucache import LruCache
 
@@ -735,8 +743,228 @@ class SlidingSyncE2eeRestServlet(RestServlet):
         return 200, response
 
 
+class SlidingSyncRestServlet(RestServlet):
+    """
+    API endpoint for MSC3575 Sliding Sync `/sync`. Allows for clients to request a
+    subset (sliding window) of rooms, state, and timeline events (just what they need)
+    in order to bootstrap quickly and subscribe to only what the client cares about.
+    Because the client can specify what it cares about, we can respond quickly and skip
+    all of the work we would normally have to do with a sync v2 response.
+
+    Request query parameters:
+        timeout: How long to wait for new events in milliseconds.
+        pos: Stream position token when asking for incremental deltas.
+
+    Request body::
+        {
+            // Sliding Window API
+            "lists": {
+                "foo-list": {
+                    "ranges": [ [0, 99] ],
+                    "sort": [ "by_notification_level", "by_recency", "by_name" ],
+                    "required_state": [
+                        ["m.room.join_rules", ""],
+                        ["m.room.history_visibility", ""],
+                        ["m.space.child", "*"]
+                    ],
+                    "timeline_limit": 10,
+                    "filters": {
+                        "is_dm": true
+                    },
+                    "bump_event_types": [ "m.room.message", "m.room.encrypted" ],
+                }
+            },
+            // Room Subscriptions API
+            "room_subscriptions": {
+                "!sub1:bar": {
+                    "required_state": [ ["*","*"] ],
+                    "timeline_limit": 10,
+                    "include_old_rooms": {
+                        "timeline_limit": 1,
+                        "required_state": [ ["m.room.tombstone", ""], ["m.room.create", ""] ],
+                    }
+                }
+            },
+            // Extensions API
+            "extensions": {}
+        }
+
+    Response JSON::
+        {
+            "next_pos": "s58_224_0_13_10_1_1_16_0_1",
+            "lists": {
+                "foo-list": {
+                    "count": 1337,
+                    "ops": [{
+                        "op": "SYNC",
+                        "range": [0, 99],
+                        "room_ids": [
+                            "!foo:bar",
+                            // ... 99 more room IDs
+                        ]
+                    }]
+                }
+            },
+            // Aggregated rooms from lists and room subscriptions
+            "rooms": {
+                // Room from room subscription
+                "!sub1:bar": {
+                    "name": "Alice and Bob",
+                    "avatar": "mxc://...",
+                    "initial": true,
+                    "required_state": [
+                        {"sender":"@alice:example.com","type":"m.room.create", "state_key":"", "content":{"creator":"@alice:example.com"}},
+                        {"sender":"@alice:example.com","type":"m.room.join_rules", "state_key":"", "content":{"join_rule":"invite"}},
+                        {"sender":"@alice:example.com","type":"m.room.history_visibility", "state_key":"", "content":{"history_visibility":"joined"}},
+                        {"sender":"@alice:example.com","type":"m.room.member", "state_key":"@alice:example.com", "content":{"membership":"join"}}
+                    ],
+                    "timeline": [
+                        {"sender":"@alice:example.com","type":"m.room.create", "state_key":"", "content":{"creator":"@alice:example.com"}},
+                        {"sender":"@alice:example.com","type":"m.room.join_rules", "state_key":"", "content":{"join_rule":"invite"}},
+                        {"sender":"@alice:example.com","type":"m.room.history_visibility", "state_key":"", "content":{"history_visibility":"joined"}},
+                        {"sender":"@alice:example.com","type":"m.room.member", "state_key":"@alice:example.com", "content":{"membership":"join"}},
+                        {"sender":"@alice:example.com","type":"m.room.message", "content":{"body":"A"}},
+                        {"sender":"@alice:example.com","type":"m.room.message", "content":{"body":"B"}},
+                    ],
+                    "prev_batch": "t111_222_333",
+                    "joined_count": 41,
+                    "invited_count": 1,
+                    "notification_count": 1,
+                    "highlight_count": 0
+                },
+                // rooms from list
+                "!foo:bar": {
+                    "name": "The calculated room name",
+                    "avatar": "mxc://...",
+                    "initial": true,
+                    "required_state": [
+                        {"sender":"@alice:example.com","type":"m.room.join_rules", "state_key":"", "content":{"join_rule":"invite"}},
+                        {"sender":"@alice:example.com","type":"m.room.history_visibility", "state_key":"", "content":{"history_visibility":"joined"}},
+                        {"sender":"@alice:example.com","type":"m.space.child", "state_key":"!foo:example.com", "content":{"via":["example.com"]}},
+                        {"sender":"@alice:example.com","type":"m.space.child", "state_key":"!bar:example.com", "content":{"via":["example.com"]}},
+                        {"sender":"@alice:example.com","type":"m.space.child", "state_key":"!baz:example.com", "content":{"via":["example.com"]}}
+                    ],
+                    "timeline": [
+                        {"sender":"@alice:example.com","type":"m.room.join_rules", "state_key":"", "content":{"join_rule":"invite"}},
+                        {"sender":"@alice:example.com","type":"m.room.message", "content":{"body":"A"}},
+                        {"sender":"@alice:example.com","type":"m.room.message", "content":{"body":"B"}},
+                        {"sender":"@alice:example.com","type":"m.room.message", "content":{"body":"C"}},
+                        {"sender":"@alice:example.com","type":"m.room.message", "content":{"body":"D"}},
+                    ],
+                    "prev_batch": "t111_222_333",
+                    "joined_count": 4,
+                    "invited_count": 0,
+                    "notification_count": 54,
+                    "highlight_count": 3
+                },
+                 // ... 99 more items
+            },
+            "extensions": {}
+        }
+    """
+
+    PATTERNS = client_patterns(
+        "/org.matrix.msc3575/sync$", releases=[], v1=False, unstable=True
+    )
+
+    def __init__(self, hs: "HomeServer"):
+        super().__init__()
+        self.auth = hs.get_auth()
+        self.store = hs.get_datastores().main
+        self.filtering = hs.get_filtering()
+        self.sliding_sync_handler = hs.get_sliding_sync_handler()
+
+    # TODO: Update this to `on_GET` once we figure out how we want to handle params
+    async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
+        requester = await self.auth.get_user_by_req(request, allow_guest=True)
+        user = requester.user
+        device_id = requester.device_id
+
+        timeout = parse_integer(request, "timeout", default=0)
+        # Position in the stream
+        from_token_string = parse_string(request, "pos")
+
+        from_token = None
+        if from_token_string is not None:
+            from_token = await StreamToken.from_string(self.store, from_token_string)
+
+        # TODO: We currently don't know whether we're going to use sticky params or
+        # maybe some filters like sync v2  where they are built up once and referenced
+        # by filter ID. For now, we will just prototype with always passing everything
+        # in.
+        body = parse_and_validate_json_object_from_request(request, SlidingSyncBody)
+        logger.info("Sliding sync request: %r", body)
+
+        sync_config = SlidingSyncConfig(
+            user=user,
+            device_id=device_id,
+            # FIXME: Currently, we're just manually copying the fields from the
+            # `SlidingSyncBody` into the config. How can we gurantee into the future
+            # that we don't forget any? I would like something more structured like
+            # `copy_attributes(from=body, to=config)`
+            lists=body.lists,
+            room_subscriptions=body.room_subscriptions,
+            extensions=body.extensions,
+        )
+
+        sliding_sync_results = await self.sliding_sync_handler.wait_for_sync_for_user(
+            requester,
+            sync_config,
+            from_token,
+            timeout,
+        )
+
+        # The client may have disconnected by now; don't bother to serialize the
+        # response if so.
+        if request._disconnected:
+            logger.info("Client has disconnected; not serializing response.")
+            return 200, {}
+
+        response_content = await self.encode_response(sliding_sync_results)
+
+        return 200, response_content
+
+    # TODO: Is there a better way to encode things?
+    async def encode_response(
+        self,
+        sliding_sync_result: SlidingSyncResult,
+    ) -> JsonDict:
+        response: JsonDict = defaultdict(dict)
+
+        response["next_pos"] = await sliding_sync_result.next_pos.to_string(self.store)
+        serialized_lists = self.encode_lists(sliding_sync_result.lists)
+        if serialized_lists:
+            response["lists"] = serialized_lists
+        response["rooms"] = {}  # TODO: sliding_sync_result.rooms
+        response["extensions"] = {}  # TODO: sliding_sync_result.extensions
+
+        return response
+
+    def encode_lists(
+        self, lists: Dict[str, SlidingSyncResult.SlidingWindowList]
+    ) -> JsonDict:
+        def encode_operation(
+            operation: SlidingSyncResult.SlidingWindowList.Operation,
+        ) -> JsonDict:
+            return {
+                "op": operation.op.value,
+                "range": operation.range,
+                "room_ids": operation.room_ids,
+            }
+
+        serialized_lists = {}
+        for list_key, list_result in lists.items():
+            serialized_lists[list_key] = {
+                "count": list_result.count,
+                "ops": [encode_operation(op) for op in list_result.ops],
+            }
+
+        return serialized_lists
+
+
 def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
     SyncRestServlet(hs).register(http_server)
 
     if hs.config.experimental.msc3575_enabled:
+        SlidingSyncRestServlet(hs).register(http_server)
         SlidingSyncE2eeRestServlet(hs).register(http_server)
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 56de6906d0..f428158139 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -149,6 +149,8 @@ class VersionsRestServlet(RestServlet):
                             is not None
                         )
                     ),
+                    # MSC4151: Report room API (Client-Server API)
+                    "org.matrix.msc4151": self.config.experimental.msc4151_enabled,
                 },
             },
         )
diff --git a/synapse/rest/key/v2/remote_key_resource.py b/synapse/rest/key/v2/remote_key_resource.py
index dc7325fc57..a411ed614e 100644
--- a/synapse/rest/key/v2/remote_key_resource.py
+++ b/synapse/rest/key/v2/remote_key_resource.py
@@ -41,9 +41,9 @@ from synapse.http.servlet import (
     parse_and_validate_json_object_from_request,
     parse_integer,
 )
-from synapse.rest.models import RequestBodyModel
 from synapse.storage.keys import FetchKeyResultForRemote
 from synapse.types import JsonDict
+from synapse.types.rest import RequestBodyModel
 from synapse.util import json_decoder
 from synapse.util.async_helpers import yieldable_gather_results
 
diff --git a/synapse/rest/media/download_resource.py b/synapse/rest/media/download_resource.py
index 8ba723c8d4..1628d58926 100644
--- a/synapse/rest/media/download_resource.py
+++ b/synapse/rest/media/download_resource.py
@@ -97,6 +97,12 @@ class DownloadResource(RestServlet):
                 respond_404(request)
                 return
 
+            ip_address = request.getClientAddress().host
             await self.media_repo.get_remote_media(
-                request, server_name, media_id, file_name, max_timeout_ms
+                request,
+                server_name,
+                media_id,
+                file_name,
+                max_timeout_ms,
+                ip_address,
             )
diff --git a/synapse/rest/media/thumbnail_resource.py b/synapse/rest/media/thumbnail_resource.py
index fe8fbb06e4..ce511c6dce 100644
--- a/synapse/rest/media/thumbnail_resource.py
+++ b/synapse/rest/media/thumbnail_resource.py
@@ -104,6 +104,7 @@ class ThumbnailResource(RestServlet):
                 respond_404(request)
                 return
 
+            ip_address = request.getClientAddress().host
             remote_resp_function = (
                 self.thumbnail_provider.select_or_generate_remote_thumbnail
                 if self.dynamic_thumbnails
@@ -118,5 +119,6 @@ class ThumbnailResource(RestServlet):
                 method,
                 m_type,
                 max_timeout_ms,
+                ip_address,
             )
             self.media_repo.mark_recently_accessed(server_name, media_id)
diff --git a/synapse/server.py b/synapse/server.py
index 95e319d2e6..ae927c3904 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -109,6 +109,7 @@ from synapse.handlers.room_summary import RoomSummaryHandler
 from synapse.handlers.search import SearchHandler
 from synapse.handlers.send_email import SendEmailHandler
 from synapse.handlers.set_password import SetPasswordHandler
+from synapse.handlers.sliding_sync import SlidingSyncHandler
 from synapse.handlers.sso import SsoHandler
 from synapse.handlers.stats import StatsHandler
 from synapse.handlers.sync import SyncHandler
@@ -554,6 +555,9 @@ class HomeServer(metaclass=abc.ABCMeta):
     def get_sync_handler(self) -> SyncHandler:
         return SyncHandler(self)
 
+    def get_sliding_sync_handler(self) -> SlidingSyncHandler:
+        return SlidingSyncHandler(self)
+
     @cache_in_self
     def get_room_list_handler(self) -> RoomListHandler:
         return RoomListHandler(self)
diff --git a/synapse/storage/controllers/state.py b/synapse/storage/controllers/state.py
index f9eced23bf..cc9b162ae4 100644
--- a/synapse/storage/controllers/state.py
+++ b/synapse/storage/controllers/state.py
@@ -45,7 +45,7 @@ from synapse.storage.util.partial_state_events_tracker import (
     PartialStateEventsTracker,
 )
 from synapse.synapse_rust.acl import ServerAclEvaluator
-from synapse.types import MutableStateMap, StateMap, get_domain_from_id
+from synapse.types import MutableStateMap, StateMap, StreamToken, get_domain_from_id
 from synapse.types.state import StateFilter
 from synapse.util.async_helpers import Linearizer
 from synapse.util.caches import intern_string
@@ -372,6 +372,91 @@ class StateStorageController:
         )
         return state_map[event_id]
 
+    async def get_state_after_event(
+        self,
+        event_id: str,
+        state_filter: Optional[StateFilter] = None,
+        await_full_state: bool = True,
+    ) -> StateMap[str]:
+        """
+        Get the room state after the given event
+
+        Args:
+            event_id: event of interest
+            state_filter: The state filter used to fetch state from the database.
+            await_full_state: if `True`, will block if we do not yet have complete state
+                at the event and `state_filter` is not satisfied by partial state.
+                Defaults to `True`.
+        """
+        state_ids = await self.get_state_ids_for_event(
+            event_id,
+            state_filter=state_filter or StateFilter.all(),
+            await_full_state=await_full_state,
+        )
+
+        # using get_metadata_for_events here (instead of get_event) sidesteps an issue
+        # with redactions: if `event_id` is a redaction event, and we don't have the
+        # original (possibly because it got purged), get_event will refuse to return
+        # the redaction event, which isn't terribly helpful here.
+        #
+        # (To be fair, in that case we could assume it's *not* a state event, and
+        # therefore we don't need to worry about it. But still, it seems cleaner just
+        # to pull the metadata.)
+        m = (await self.stores.main.get_metadata_for_events([event_id]))[event_id]
+        if m.state_key is not None and m.rejection_reason is None:
+            state_ids = dict(state_ids)
+            state_ids[(m.event_type, m.state_key)] = event_id
+
+        return state_ids
+
+    async def get_state_at(
+        self,
+        room_id: str,
+        stream_position: StreamToken,
+        state_filter: Optional[StateFilter] = None,
+        await_full_state: bool = True,
+    ) -> StateMap[str]:
+        """Get the room state at a particular stream position
+
+        Args:
+            room_id: room for which to get state
+            stream_position: point at which to get state
+            state_filter: The state filter used to fetch state from the database.
+            await_full_state: if `True`, will block if we do not yet have complete state
+                at the last event in the room before `stream_position` and
+                `state_filter` is not satisfied by partial state. Defaults to `True`.
+        """
+        # FIXME: This gets the state at the latest event before the stream ordering,
+        # which might not be the same as the "current state" of the room at the time
+        # of the stream token if there were multiple forward extremities at the time.
+        last_event_id = (
+            await self.stores.main.get_last_event_id_in_room_before_stream_ordering(
+                room_id,
+                end_token=stream_position.room_key,
+            )
+        )
+
+        if last_event_id:
+            state = await self.get_state_after_event(
+                last_event_id,
+                state_filter=state_filter or StateFilter.all(),
+                await_full_state=await_full_state,
+            )
+
+        else:
+            # no events in this room - so presumably no state
+            state = {}
+
+            # (erikj) This should be rarely hit, but we've had some reports that
+            # we get more state down gappy syncs than we should, so let's add
+            # some logging.
+            logger.info(
+                "Failed to find any events in room %s at %s",
+                room_id,
+                stream_position.room_key,
+            )
+        return state
+
     @trace
     @tag_args
     async def get_state_for_groups(
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index f1bd85aa27..66428e6c8e 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -207,6 +207,7 @@ class PersistEventsStore:
         async with stream_ordering_manager as stream_orderings:
             for (event, _), stream in zip(events_and_contexts, stream_orderings):
                 event.internal_metadata.stream_ordering = stream
+                event.internal_metadata.instance_name = self._instance_name
 
             await self.db_pool.runInteraction(
                 "persist_events",
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index c06c44deb1..e264d36f02 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -156,6 +156,7 @@ class _EventRow:
 
     event_id: str
     stream_ordering: int
+    instance_name: str
     json: str
     internal_metadata: str
     format_version: Optional[int]
@@ -1354,6 +1355,7 @@ class EventsWorkerStore(SQLBaseStore):
                 rejected_reason=rejected_reason,
             )
             original_ev.internal_metadata.stream_ordering = row.stream_ordering
+            original_ev.internal_metadata.instance_name = row.instance_name
             original_ev.internal_metadata.outlier = row.outlier
 
             # Consistency check: if the content of the event has been modified in the
@@ -1439,6 +1441,7 @@ class EventsWorkerStore(SQLBaseStore):
                 SELECT
                   e.event_id,
                   e.stream_ordering,
+                  e.instance_name,
                   ej.internal_metadata,
                   ej.json,
                   ej.format_version,
@@ -1462,13 +1465,14 @@ class EventsWorkerStore(SQLBaseStore):
                 event_dict[event_id] = _EventRow(
                     event_id=event_id,
                     stream_ordering=row[1],
-                    internal_metadata=row[2],
-                    json=row[3],
-                    format_version=row[4],
-                    room_version_id=row[5],
-                    rejected_reason=row[6],
+                    instance_name=row[2],
+                    internal_metadata=row[3],
+                    json=row[4],
+                    format_version=row[5],
+                    room_version_id=row[6],
+                    rejected_reason=row[7],
                     redactions=[],
-                    outlier=bool(row[7]),  # This is an int in SQLite3
+                    outlier=bool(row[8]),  # This is an int in SQLite3
                 )
 
             # check for redactions
diff --git a/synapse/storage/databases/main/room.py b/synapse/storage/databases/main/room.py
index 616c941687..b8a71c803e 100644
--- a/synapse/storage/databases/main/room.py
+++ b/synapse/storage/databases/main/room.py
@@ -2207,6 +2207,7 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         super().__init__(database, db_conn, hs)
 
         self._event_reports_id_gen = IdGenerator(db_conn, "event_reports", "id")
+        self._room_reports_id_gen = IdGenerator(db_conn, "room_reports", "id")
 
         self._instance_name = hs.get_instance_name()
 
@@ -2416,6 +2417,37 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore):
         )
         return next_id
 
+    async def add_room_report(
+        self,
+        room_id: str,
+        user_id: str,
+        reason: str,
+        received_ts: int,
+    ) -> int:
+        """Add a room report
+
+        Args:
+            room_id: The room ID being reported.
+            user_id: User who reports the room.
+            reason: Description that the user specifies.
+            received_ts: Time when the user submitted the report (milliseconds).
+        Returns:
+            Id of the room report.
+        """
+        next_id = self._room_reports_id_gen.get_next()
+        await self.db_pool.simple_insert(
+            table="room_reports",
+            values={
+                "id": next_id,
+                "received_ts": received_ts,
+                "room_id": room_id,
+                "user_id": user_id,
+                "reason": reason,
+            },
+            desc="add_room_report",
+        )
+        return next_id
+
     async def block_room(self, room_id: str, user_id: str) -> None:
         """Marks the room as blocked.
 
diff --git a/synapse/storage/databases/main/roommember.py b/synapse/storage/databases/main/roommember.py
index 9fddbb2caf..d8b54dc4e3 100644
--- a/synapse/storage/databases/main/roommember.py
+++ b/synapse/storage/databases/main/roommember.py
@@ -476,7 +476,7 @@ class RoomMemberWorkerStore(EventsWorkerStore, CacheInvalidationWorkerStore):
         )
 
         sql = """
-            SELECT room_id, e.sender, c.membership, event_id, e.stream_ordering, r.room_version
+            SELECT room_id, e.sender, c.membership, event_id, e.instance_name, e.stream_ordering, r.room_version
             FROM local_current_membership AS c
             INNER JOIN events AS e USING (room_id, event_id)
             INNER JOIN rooms AS r USING (room_id)
@@ -488,7 +488,17 @@ class RoomMemberWorkerStore(EventsWorkerStore, CacheInvalidationWorkerStore):
         )
 
         txn.execute(sql, (user_id, *args))
-        results = [RoomsForUser(*r) for r in txn]
+        results = [
+            RoomsForUser(
+                room_id=room_id,
+                sender=sender,
+                membership=membership,
+                event_id=event_id,
+                event_pos=PersistedEventPosition(instance_name, stream_ordering),
+                room_version_id=room_version,
+            )
+            for room_id, sender, membership, event_id, instance_name, stream_ordering, room_version in txn
+        ]
 
         return results
 
diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py
index 7ab6003f61..ff0d723684 100644
--- a/synapse/storage/databases/main/stream.py
+++ b/synapse/storage/databases/main/stream.py
@@ -895,7 +895,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             "get_room_event_before_stream_ordering", _f
         )
 
-    async def get_last_event_in_room_before_stream_ordering(
+    async def get_last_event_id_in_room_before_stream_ordering(
         self,
         room_id: str,
         end_token: RoomStreamToken,
@@ -910,16 +910,55 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             The ID of the most recent event, or None if there are no events in the room
             before this stream ordering.
         """
+        last_event_result = (
+            await self.get_last_event_pos_in_room_before_stream_ordering(
+                room_id, end_token
+            )
+        )
 
-        def get_last_event_in_room_before_stream_ordering_txn(
-            txn: LoggingTransaction,
-        ) -> Optional[str]:
-            # We need to handle the fact that the stream tokens can be vector
-            # clocks. We do this by getting all rows between the minimum and
-            # maximum stream ordering in the token, plus one row less than the
-            # minimum stream ordering. We then filter the results against the
-            # token and return the first row that matches.
+        if last_event_result:
+            return last_event_result[0]
+
+        return None
+
+    async def get_last_event_pos_in_room_before_stream_ordering(
+        self,
+        room_id: str,
+        end_token: RoomStreamToken,
+    ) -> Optional[Tuple[str, PersistedEventPosition]]:
+        """
+        Returns the ID and event position of the last event in a room at or before a
+        stream ordering.
 
+        Args:
+            room_id
+            end_token: The token used to stream from
+
+        Returns:
+            The ID of the most recent event and it's position, or None if there are no
+            events in the room before this stream ordering.
+        """
+
+        def get_last_event_pos_in_room_before_stream_ordering_txn(
+            txn: LoggingTransaction,
+        ) -> Optional[Tuple[str, PersistedEventPosition]]:
+            # We're looking for the closest event at or before the token. We need to
+            # handle the fact that the stream token can be a vector clock (with an
+            # `instance_map`) and events can be persisted on different instances
+            # (sharded event persisters). The first subquery handles the events that
+            # would be within the vector clock and gets all rows between the minimum and
+            # maximum stream ordering in the token which need to be filtered against the
+            # `instance_map`. The second subquery handles the "before" case and finds
+            # the first row before the token. We then filter out any results past the
+            # token's vector clock and return the first row that matches.
+            min_stream = end_token.stream
+            max_stream = end_token.get_max_stream_pos()
+
+            # We use `union all` because we don't need any of the deduplication logic
+            # (`union` is really a union + distinct). `UNION ALL` does preserve the
+            # ordering of the operand queries but there is no actual gurantee that it
+            # has this behavior in all scenarios so we need the extra `ORDER BY` at the
+            # bottom.
             sql = """
                 SELECT * FROM (
                     SELECT instance_name, stream_ordering, topological_ordering, event_id
@@ -931,7 +970,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
                         AND rejections.event_id IS NULL
                     ORDER BY stream_ordering DESC
                 ) AS a
-                UNION
+                UNION ALL
                 SELECT * FROM (
                     SELECT instance_name, stream_ordering, topological_ordering, event_id
                     FROM events
@@ -943,15 +982,16 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
                     ORDER BY stream_ordering DESC
                     LIMIT 1
                 ) AS b
+                ORDER BY stream_ordering DESC
             """
             txn.execute(
                 sql,
                 (
                     room_id,
-                    end_token.stream,
-                    end_token.get_max_stream_pos(),
+                    min_stream,
+                    max_stream,
                     room_id,
-                    end_token.stream,
+                    min_stream,
                 ),
             )
 
@@ -963,13 +1003,15 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
                     topological_ordering=topological_ordering,
                     stream_ordering=stream_ordering,
                 ):
-                    return event_id
+                    return event_id, PersistedEventPosition(
+                        instance_name, stream_ordering
+                    )
 
             return None
 
         return await self.db_pool.runInteraction(
-            "get_last_event_in_room_before_stream_ordering",
-            get_last_event_in_room_before_stream_ordering_txn,
+            "get_last_event_pos_in_room_before_stream_ordering",
+            get_last_event_pos_in_room_before_stream_ordering_txn,
         )
 
     async def get_current_room_stream_token_for_room_id(
diff --git a/synapse/storage/databases/main/user_directory.py b/synapse/storage/databases/main/user_directory.py
index 0513e7dc06..6e18f714d7 100644
--- a/synapse/storage/databases/main/user_directory.py
+++ b/synapse/storage/databases/main/user_directory.py
@@ -1281,7 +1281,7 @@ def _parse_words_with_regex(search_term: str) -> List[str]:
     Break down search term into words, when we don't have ICU available.
     See: `_parse_words`
     """
-    return re.findall(r"([\w\-]+)", search_term, re.UNICODE)
+    return re.findall(r"([\w-]+)", search_term, re.UNICODE)
 
 
 def _parse_words_with_icu(search_term: str) -> List[str]:
@@ -1303,15 +1303,69 @@ def _parse_words_with_icu(search_term: str) -> List[str]:
         if j < 0:
             break
 
-        result = search_term[i:j]
+        # We want to make sure that we split on `@` and `:` specifically, as
+        # they occur in user IDs.
+        for result in re.split(r"[@:]+", search_term[i:j]):
+            results.append(result.strip())
+
+        i = j
+
+    # libicu will break up words that have punctuation in them, but to handle
+    # cases where user IDs have '-', '.' and '_' in them we want to *not* break
+    # those into words and instead allow the DB to tokenise them how it wants.
+    #
+    # In particular, user-71 in postgres gets tokenised to "user, -71", and this
+    # will not match a query for "user, 71".
+    new_results: List[str] = []
+    i = 0
+    while i < len(results):
+        curr = results[i]
+
+        prev = None
+        next = None
+        if i > 0:
+            prev = results[i - 1]
+        if i + 1 < len(results):
+            next = results[i + 1]
+
+        i += 1
 
         # libicu considers spaces and punctuation between words as words, but we don't
         # want to include those in results as they would result in syntax errors in SQL
         # queries (e.g. "foo bar" would result in the search query including "foo &  &
         # bar").
-        if len(re.findall(r"([\w\-]+)", result, re.UNICODE)):
-            results.append(result)
+        if not curr:
+            continue
+
+        if curr in ["-", ".", "_"]:
+            prefix = ""
+            suffix = ""
+
+            # Check if the next item is a word, and if so use it as the suffix.
+            # We check for if its a word as we don't want to concatenate
+            # multiple punctuation marks.
+            if next is not None and re.match(r"\w", next):
+                suffix = next
+                i += 1  # We're using next, so we skip it in the outer loop.
+            else:
+                # We want to avoid creating terms like "user-", as we should
+                # strip trailing punctuation.
+                continue
 
-        i = j
+            if prev and re.match(r"\w", prev) and new_results:
+                prefix = new_results[-1]
+                new_results.pop()
+
+            # We might not have a prefix here, but that's fine as we want to
+            # ensure that we don't strip preceding punctuation e.g. '-71'
+            # shouldn't be converted to '71'.
+
+            new_results.append(f"{prefix}{curr}{suffix}")
+            continue
+        elif not re.match(r"\w", curr):
+            # Ignore other punctuation
+            continue
+
+        new_results.append(curr)
 
-    return results
+    return new_results
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 7471f81a19..80c9630867 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -35,7 +35,7 @@ class RoomsForUser:
     sender: str
     membership: str
     event_id: str
-    stream_ordering: int
+    event_pos: PersistedEventPosition
     room_version_id: str
 
 
diff --git a/synapse/storage/schema/main/delta/85/06_add_room_reports.sql b/synapse/storage/schema/main/delta/85/06_add_room_reports.sql
new file mode 100644
index 0000000000..f7b45276cf
--- /dev/null
+++ b/synapse/storage/schema/main/delta/85/06_add_room_reports.sql
@@ -0,0 +1,20 @@
+--
+-- This file is licensed under the Affero General Public License (AGPL) version 3.
+--
+-- Copyright (C) 2024 New Vector, Ltd
+--
+-- This program is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU Affero General Public License as
+-- published by the Free Software Foundation, either version 3 of the
+-- License, or (at your option) any later version.
+--
+-- See the GNU Affero General Public License for more details:
+-- <https://www.gnu.org/licenses/agpl-3.0.html>.
+
+CREATE TABLE room_reports (
+    id BIGINT NOT NULL PRIMARY KEY,
+    received_ts BIGINT NOT NULL,
+    room_id TEXT NOT NULL,
+    user_id TEXT NOT NULL,
+    reason TEXT NOT NULL
+);
diff --git a/synapse/synapse_rust/events.pyi b/synapse/synapse_rust/events.pyi
index 69837617f5..1682d0d151 100644
--- a/synapse/synapse_rust/events.pyi
+++ b/synapse/synapse_rust/events.pyi
@@ -19,6 +19,8 @@ class EventInternalMetadata:
 
     stream_ordering: Optional[int]
     """the stream ordering of this event. None, until it has been persisted."""
+    instance_name: Optional[str]
+    """the instance name of the server that persisted this event. None, until it has been persisted."""
 
     outlier: bool
     """whether this event is an outlier (ie, whether we have the state at that
diff --git a/synapse/types/handlers/__init__.py b/synapse/types/handlers/__init__.py
new file mode 100644
index 0000000000..1d65551d5b
--- /dev/null
+++ b/synapse/types/handlers/__init__.py
@@ -0,0 +1,252 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2024 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# Originally licensed under the Apache License, Version 2.0:
+# <http://www.apache.org/licenses/LICENSE-2.0>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+from enum import Enum
+from typing import TYPE_CHECKING, Dict, Final, List, Optional, Tuple
+
+import attr
+from typing_extensions import TypedDict
+
+from synapse._pydantic_compat import HAS_PYDANTIC_V2
+
+if TYPE_CHECKING or HAS_PYDANTIC_V2:
+    from pydantic.v1 import Extra
+else:
+    from pydantic import Extra
+
+from synapse.events import EventBase
+from synapse.types import JsonMapping, StreamToken, UserID
+from synapse.types.rest.client import SlidingSyncBody
+
+
+class ShutdownRoomParams(TypedDict):
+    """
+    Attributes:
+        requester_user_id:
+            User who requested the action. Will be recorded as putting the room on the
+            blocking list.
+        new_room_user_id:
+            If set, a new room will be created with this user ID
+            as the creator and admin, and all users in the old room will be
+            moved into that room. If not set, no new room will be created
+            and the users will just be removed from the old room.
+        new_room_name:
+            A string representing the name of the room that new users will
+            be invited to. Defaults to `Content Violation Notification`
+        message:
+            A string containing the first message that will be sent as
+            `new_room_user_id` in the new room. Ideally this will clearly
+            convey why the original room was shut down.
+            Defaults to `Sharing illegal content on this server is not
+            permitted and rooms in violation will be blocked.`
+        block:
+            If set to `true`, this room will be added to a blocking list,
+            preventing future attempts to join the room. Defaults to `false`.
+        purge:
+            If set to `true`, purge the given room from the database.
+        force_purge:
+            If set to `true`, the room will be purged from database
+            even if there are still users joined to the room.
+    """
+
+    requester_user_id: Optional[str]
+    new_room_user_id: Optional[str]
+    new_room_name: Optional[str]
+    message: Optional[str]
+    block: bool
+    purge: bool
+    force_purge: bool
+
+
+class ShutdownRoomResponse(TypedDict):
+    """
+    Attributes:
+        kicked_users: An array of users (`user_id`) that were kicked.
+        failed_to_kick_users:
+            An array of users (`user_id`) that that were not kicked.
+        local_aliases:
+            An array of strings representing the local aliases that were
+            migrated from the old room to the new.
+        new_room_id: A string representing the room ID of the new room.
+    """
+
+    kicked_users: List[str]
+    failed_to_kick_users: List[str]
+    local_aliases: List[str]
+    new_room_id: Optional[str]
+
+
+class SlidingSyncConfig(SlidingSyncBody):
+    """
+    Inherit from `SlidingSyncBody` since we need all of the same fields and add a few
+    extra fields that we need in the handler
+    """
+
+    user: UserID
+    device_id: Optional[str]
+
+    # Pydantic config
+    class Config:
+        # By default, ignore fields that we don't recognise.
+        extra = Extra.ignore
+        # By default, don't allow fields to be reassigned after parsing.
+        allow_mutation = False
+        # Allow custom types like `UserID` to be used in the model
+        arbitrary_types_allowed = True
+
+
+class OperationType(Enum):
+    """
+    Represents the operation types in a Sliding Sync window.
+
+    Attributes:
+        SYNC: Sets a range of entries. Clients SHOULD discard what they previous knew about
+            entries in this range.
+        INSERT: Sets a single entry. If the position is not empty then clients MUST move
+            entries to the left or the right depending on where the closest empty space is.
+        DELETE: Remove a single entry. Often comes before an INSERT to allow entries to move
+            places.
+        INVALIDATE: Remove a range of entries. Clients MAY persist the invalidated range for
+            offline support, but they should be treated as empty when additional operations
+            which concern indexes in the range arrive from the server.
+    """
+
+    SYNC: Final = "SYNC"
+    INSERT: Final = "INSERT"
+    DELETE: Final = "DELETE"
+    INVALIDATE: Final = "INVALIDATE"
+
+
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class SlidingSyncResult:
+    """
+    The Sliding Sync result to be serialized to JSON for a response.
+
+    Attributes:
+        next_pos: The next position token in the sliding window to request (next_batch).
+        lists: Sliding window API. A map of list key to list results.
+        rooms: Room subscription API. A map of room ID to room subscription to room results.
+        extensions: Extensions API. A map of extension key to extension results.
+    """
+
+    @attr.s(slots=True, frozen=True, auto_attribs=True)
+    class RoomResult:
+        """
+        Attributes:
+            name: Room name or calculated room name.
+            avatar: Room avatar
+            heroes: List of stripped membership events (containing `user_id` and optionally
+                `avatar_url` and `displayname`) for the users used to calculate the room name.
+            initial: Flag which is set when this is the first time the server is sending this
+                data on this connection. Clients can use this flag to replace or update
+                their local state. When there is an update, servers MUST omit this flag
+                entirely and NOT send "initial":false as this is wasteful on bandwidth. The
+                absence of this flag means 'false'.
+            required_state: The current state of the room
+            timeline: Latest events in the room. The last event is the most recent
+            is_dm: Flag to specify whether the room is a direct-message room (most likely
+                between two people).
+            invite_state: Stripped state events. Same as `rooms.invite.$room_id.invite_state`
+                in sync v2, absent on joined/left rooms
+            prev_batch: A token that can be passed as a start parameter to the
+                `/rooms/<room_id>/messages` API to retrieve earlier messages.
+            limited: True if their are more events than fit between the given position and now.
+                Sync again to get more.
+            joined_count: The number of users with membership of join, including the client's
+                own user ID. (same as sync `v2 m.joined_member_count`)
+            invited_count: The number of users with membership of invite. (same as sync v2
+                `m.invited_member_count`)
+            notification_count: The total number of unread notifications for this room. (same
+                as sync v2)
+            highlight_count: The number of unread notifications for this room with the highlight
+                flag set. (same as sync v2)
+            num_live: The number of timeline events which have just occurred and are not historical.
+                The last N events are 'live' and should be treated as such. This is mostly
+                useful to determine whether a given @mention event should make a noise or not.
+                Clients cannot rely solely on the absence of `initial: true` to determine live
+                events because if a room not in the sliding window bumps into the window because
+                of an @mention it will have `initial: true` yet contain a single live event
+                (with potentially other old events in the timeline).
+        """
+
+        name: str
+        avatar: Optional[str]
+        heroes: Optional[List[EventBase]]
+        initial: bool
+        required_state: List[EventBase]
+        timeline: List[EventBase]
+        is_dm: bool
+        invite_state: List[EventBase]
+        prev_batch: StreamToken
+        limited: bool
+        joined_count: int
+        invited_count: int
+        notification_count: int
+        highlight_count: int
+        num_live: int
+
+    @attr.s(slots=True, frozen=True, auto_attribs=True)
+    class SlidingWindowList:
+        """
+        Attributes:
+            count: The total number of entries in the list. Always present if this list
+                is.
+            ops: The sliding list operations to perform.
+        """
+
+        @attr.s(slots=True, frozen=True, auto_attribs=True)
+        class Operation:
+            """
+            Attributes:
+                op: The operation type to perform.
+                range: Which index positions are affected by this operation. These are
+                    both inclusive.
+                room_ids: Which room IDs are affected by this operation. These IDs match
+                    up to the positions in the `range`, so the last room ID in this list
+                    matches the 9th index. The room data is held in a separate object.
+            """
+
+            op: OperationType
+            range: Tuple[int, int]
+            room_ids: List[str]
+
+        count: int
+        ops: List[Operation]
+
+    next_pos: StreamToken
+    lists: Dict[str, SlidingWindowList]
+    rooms: Dict[str, RoomResult]
+    extensions: JsonMapping
+
+    def __bool__(self) -> bool:
+        """Make the result appear empty if there are no updates. This is used
+        to tell if the notifier needs to wait for more events when polling for
+        events.
+        """
+        return bool(self.lists or self.rooms or self.extensions)
+
+    @staticmethod
+    def empty(next_pos: StreamToken) -> "SlidingSyncResult":
+        "Return a new empty result"
+        return SlidingSyncResult(
+            next_pos=next_pos,
+            lists={},
+            rooms={},
+            extensions={},
+        )
diff --git a/synapse/rest/models.py b/synapse/types/rest/__init__.py
index 2b6f5ed35a..2b6f5ed35a 100644
--- a/synapse/rest/models.py
+++ b/synapse/types/rest/__init__.py
diff --git a/synapse/types/rest/client/__init__.py b/synapse/types/rest/client/__init__.py
new file mode 100644
index 0000000000..e2c79c4106
--- /dev/null
+++ b/synapse/types/rest/client/__init__.py
@@ -0,0 +1,309 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+# Copyright (C) 2023 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# Originally licensed under the Apache License, Version 2.0:
+# <http://www.apache.org/licenses/LICENSE-2.0>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+from typing import TYPE_CHECKING, Dict, List, Optional, Tuple, Union
+
+from synapse._pydantic_compat import HAS_PYDANTIC_V2
+
+if TYPE_CHECKING or HAS_PYDANTIC_V2:
+    from pydantic.v1 import (
+        Extra,
+        StrictBool,
+        StrictInt,
+        StrictStr,
+        conint,
+        constr,
+        validator,
+    )
+else:
+    from pydantic import (
+        Extra,
+        StrictBool,
+        StrictInt,
+        StrictStr,
+        conint,
+        constr,
+        validator,
+    )
+
+from synapse.types.rest import RequestBodyModel
+from synapse.util.threepids import validate_email
+
+
+class AuthenticationData(RequestBodyModel):
+    """
+    Data used during user-interactive authentication.
+
+    (The name "Authentication Data" is taken directly from the spec.)
+
+    Additional keys will be present, depending on the `type` field. Use
+    `.dict(exclude_unset=True)` to access them.
+    """
+
+    class Config:
+        extra = Extra.allow
+
+    session: Optional[StrictStr] = None
+    type: Optional[StrictStr] = None
+
+
+if TYPE_CHECKING:
+    ClientSecretStr = StrictStr
+else:
+    # See also assert_valid_client_secret()
+    ClientSecretStr = constr(
+        regex="[0-9a-zA-Z.=_-]",  # noqa: F722
+        min_length=1,
+        max_length=255,
+        strict=True,
+    )
+
+
+class ThreepidRequestTokenBody(RequestBodyModel):
+    client_secret: ClientSecretStr
+    id_server: Optional[StrictStr]
+    id_access_token: Optional[StrictStr]
+    next_link: Optional[StrictStr]
+    send_attempt: StrictInt
+
+    @validator("id_access_token", always=True)
+    def token_required_for_identity_server(
+        cls, token: Optional[str], values: Dict[str, object]
+    ) -> Optional[str]:
+        if values.get("id_server") is not None and token is None:
+            raise ValueError("id_access_token is required if an id_server is supplied.")
+        return token
+
+
+class EmailRequestTokenBody(ThreepidRequestTokenBody):
+    email: StrictStr
+
+    # Canonicalise the email address. The addresses are all stored canonicalised
+    # in the database. This allows the user to reset his password without having to
+    # know the exact spelling (eg. upper and lower case) of address in the database.
+    # Without this, an email stored in the database as "foo@bar.com" would cause
+    # user requests for "FOO@bar.com" to raise a Not Found error.
+    _email_validator = validator("email", allow_reuse=True)(validate_email)
+
+
+if TYPE_CHECKING:
+    ISO3116_1_Alpha_2 = StrictStr
+else:
+    # Per spec: two-letter uppercase ISO-3166-1-alpha-2
+    ISO3116_1_Alpha_2 = constr(regex="[A-Z]{2}", strict=True)
+
+
+class MsisdnRequestTokenBody(ThreepidRequestTokenBody):
+    country: ISO3116_1_Alpha_2
+    phone_number: StrictStr
+
+
+class SlidingSyncBody(RequestBodyModel):
+    """
+    Sliding Sync API request body.
+
+    Attributes:
+        lists: Sliding window API. A map of list key to list information
+            (:class:`SlidingSyncList`). Max lists: 100. The list keys should be
+            arbitrary strings which the client is using to refer to the list. Keep this
+            small as it needs to be sent a lot. Max length: 64 bytes.
+        room_subscriptions: Room subscription API. A map of room ID to room subscription
+            information. Used to subscribe to a specific room. Sometimes clients know
+            exactly which room they want to get information about e.g by following a
+            permalink or by refreshing a webapp currently viewing a specific room. The
+            sliding window API alone is insufficient for this use case because there's
+            no way to say "please track this room explicitly".
+        extensions: Extensions API. A map of extension key to extension config.
+    """
+
+    class CommonRoomParameters(RequestBodyModel):
+        """
+        Common parameters shared between the sliding window and room subscription APIs.
+
+        Attributes:
+            required_state: Required state for each room returned. An array of event
+                type and state key tuples. Elements in this array are ORd together to
+                produce the final set of state events to return. One unique exception is
+                when you request all state events via `["*", "*"]`. When used, all state
+                events are returned by default, and additional entries FILTER OUT the
+                returned set of state events. These additional entries cannot use `*`
+                themselves. For example, `["*", "*"], ["m.room.member",
+                "@alice:example.com"]` will *exclude* every `m.room.member` event
+                *except* for `@alice:example.com`, and include every other state event.
+                In addition, `["*", "*"], ["m.space.child", "*"]` is an error, the
+                `m.space.child` filter is not required as it would have been returned
+                anyway.
+            timeline_limit: The maximum number of timeline events to return per response.
+                (Max 1000 messages)
+            include_old_rooms: Determines if `predecessor` rooms are included in the
+                `rooms` response. The user MUST be joined to old rooms for them to show up
+                in the response.
+        """
+
+        class IncludeOldRooms(RequestBodyModel):
+            timeline_limit: StrictInt
+            required_state: List[Tuple[StrictStr, StrictStr]]
+
+        required_state: List[Tuple[StrictStr, StrictStr]]
+        # mypy workaround via https://github.com/pydantic/pydantic/issues/156#issuecomment-1130883884
+        if TYPE_CHECKING:
+            timeline_limit: int
+        else:
+            timeline_limit: conint(le=1000, strict=True)  # type: ignore[valid-type]
+        include_old_rooms: Optional[IncludeOldRooms] = None
+
+    class SlidingSyncList(CommonRoomParameters):
+        """
+        Attributes:
+            ranges: Sliding window ranges. If this field is missing, no sliding window
+                is used and all rooms are returned in this list. Integers are
+                *inclusive*.
+            slow_get_all_rooms: Just get all rooms (for clients that don't want to deal with
+                sliding windows). When true, the `ranges` field is ignored.
+            required_state: Required state for each room returned. An array of event
+                type and state key tuples. Elements in this array are ORd together to
+                produce the final set of state events to return.
+
+                One unique exception is when you request all state events via `["*",
+                "*"]`. When used, all state events are returned by default, and
+                additional entries FILTER OUT the returned set of state events. These
+                additional entries cannot use `*` themselves. For example, `["*", "*"],
+                ["m.room.member", "@alice:example.com"]` will *exclude* every
+                `m.room.member` event *except* for `@alice:example.com`, and include
+                every other state event. In addition, `["*", "*"], ["m.space.child",
+                "*"]` is an error, the `m.space.child` filter is not required as it
+                would have been returned anyway.
+
+                Room members can be lazily-loaded by using the special `$LAZY` state key
+                (`["m.room.member", "$LAZY"]`). Typically, when you view a room, you
+                want to retrieve all state events except for m.room.member events which
+                you want to lazily load. To get this behaviour, clients can send the
+                following::
+
+                    {
+                        "required_state": [
+                            // activate lazy loading
+                            ["m.room.member", "$LAZY"],
+                            // request all state events _except_ for m.room.member
+                            events which are lazily loaded
+                            ["*", "*"]
+                        ]
+                    }
+
+            timeline_limit: The maximum number of timeline events to return per response.
+            include_old_rooms: Determines if `predecessor` rooms are included in the
+                `rooms` response. The user MUST be joined to old rooms for them to show up
+                in the response.
+            include_heroes: Return a stripped variant of membership events (containing
+                `user_id` and optionally `avatar_url` and `displayname`) for the users used
+                to calculate the room name.
+            filters: Filters to apply to the list before sorting.
+        """
+
+        class Filters(RequestBodyModel):
+            """
+            All fields are applied with AND operators, hence if `is_dm: True` and
+            `is_encrypted: True` then only Encrypted DM rooms will be returned. The
+            absence of fields implies no filter on that criteria: it does NOT imply
+            `False`. These fields may be expanded through use of extensions.
+
+            Attributes:
+                is_dm: Flag which only returns rooms present (or not) in the DM section
+                    of account data. If unset, both DM rooms and non-DM rooms are returned.
+                    If False, only non-DM rooms are returned. If True, only DM rooms are
+                    returned.
+                spaces: Filter the room based on the space they belong to according to
+                    `m.space.child` state events. If multiple spaces are present, a room can
+                    be part of any one of the listed spaces (OR'd). The server will inspect
+                    the `m.space.child` state events for the JOINED space room IDs given.
+                    Servers MUST NOT navigate subspaces. It is up to the client to give a
+                    complete list of spaces to navigate. Only rooms directly mentioned as
+                    `m.space.child` events in these spaces will be returned. Unknown spaces
+                    or spaces the user is not joined to will be ignored.
+                is_encrypted: Flag which only returns rooms which have an
+                    `m.room.encryption` state event. If unset, both encrypted and
+                    unencrypted rooms are returned. If `False`, only unencrypted rooms are
+                    returned. If `True`, only encrypted rooms are returned.
+                is_invite: Flag which only returns rooms the user is currently invited
+                    to. If unset, both invited and joined rooms are returned. If `False`, no
+                    invited rooms are returned. If `True`, only invited rooms are returned.
+                room_types: If specified, only rooms where the `m.room.create` event has
+                    a `type` matching one of the strings in this array will be returned. If
+                    this field is unset, all rooms are returned regardless of type. This can
+                    be used to get the initial set of spaces for an account. For rooms which
+                    do not have a room type, use `null`/`None` to include them.
+                not_room_types: Same as `room_types` but inverted. This can be used to
+                    filter out spaces from the room list. If a type is in both `room_types`
+                    and `not_room_types`, then `not_room_types` wins and they are not included
+                    in the result.
+                room_name_like: Filter the room name. Case-insensitive partial matching
+                    e.g 'foo' matches 'abFooab'. The term 'like' is inspired by SQL 'LIKE',
+                    and the text here is similar to '%foo%'.
+                tags: Filter the room based on its room tags. If multiple tags are
+                    present, a room can have any one of the listed tags (OR'd).
+                not_tags: Filter the room based on its room tags. Takes priority over
+                    `tags`. For example, a room with tags A and B with filters `tags: [A]`
+                    `not_tags: [B]` would NOT be included because `not_tags` takes priority over
+                    `tags`. This filter is useful if your rooms list does NOT include the
+                    list of favourite rooms again.
+            """
+
+            is_dm: Optional[StrictBool] = None
+            spaces: Optional[List[StrictStr]] = None
+            is_encrypted: Optional[StrictBool] = None
+            is_invite: Optional[StrictBool] = None
+            room_types: Optional[List[Union[StrictStr, None]]] = None
+            not_room_types: Optional[List[StrictStr]] = None
+            room_name_like: Optional[StrictStr] = None
+            tags: Optional[List[StrictStr]] = None
+            not_tags: Optional[List[StrictStr]] = None
+
+        # mypy workaround via https://github.com/pydantic/pydantic/issues/156#issuecomment-1130883884
+        if TYPE_CHECKING:
+            ranges: Optional[List[Tuple[int, int]]] = None
+        else:
+            ranges: Optional[List[Tuple[conint(ge=0, strict=True), conint(ge=0, strict=True)]]] = None  # type: ignore[valid-type]
+        slow_get_all_rooms: Optional[StrictBool] = False
+        include_heroes: Optional[StrictBool] = False
+        filters: Optional[Filters] = None
+
+    class RoomSubscription(CommonRoomParameters):
+        pass
+
+    class Extension(RequestBodyModel):
+        enabled: Optional[StrictBool] = False
+        lists: Optional[List[StrictStr]] = None
+        rooms: Optional[List[StrictStr]] = None
+
+    # mypy workaround via https://github.com/pydantic/pydantic/issues/156#issuecomment-1130883884
+    if TYPE_CHECKING:
+        lists: Optional[Dict[str, SlidingSyncList]] = None
+    else:
+        lists: Optional[Dict[constr(max_length=64, strict=True), SlidingSyncList]] = None  # type: ignore[valid-type]
+    room_subscriptions: Optional[Dict[StrictStr, RoomSubscription]] = None
+    extensions: Optional[Dict[StrictStr, Extension]] = None
+
+    @validator("lists")
+    def lists_length_check(
+        cls, value: Optional[Dict[str, SlidingSyncList]]
+    ) -> Optional[Dict[str, SlidingSyncList]]:
+        if value is not None:
+            assert len(value) <= 100, f"Max lists: 100 but saw {len(value)}"
+        return value
diff --git a/synapse/visibility.py b/synapse/visibility.py
index 09a947ef15..128413c8aa 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -82,7 +82,6 @@ async def filter_events_for_client(
     is_peeking: bool = False,
     always_include_ids: FrozenSet[str] = frozenset(),
     filter_send_to_client: bool = True,
-    msc4115_membership_on_events: bool = False,
 ) -> List[EventBase]:
     """
     Check which events a user is allowed to see. If the user can see the event but its
@@ -101,12 +100,10 @@ async def filter_events_for_client(
         filter_send_to_client: Whether we're checking an event that's going to be
             sent to a client. This might not always be the case since this function can
             also be called to check whether a user can see the state at a given point.
-        msc4115_membership_on_events: Whether to include the requesting user's
-            membership in the "unsigned" data, per MSC4115.
 
     Returns:
-        The filtered events. If `msc4115_membership_on_events` is true, the `unsigned`
-        data is annotated with the membership state of `user_id` at each event.
+        The filtered events. The `unsigned` data is annotated with the membership state
+        of `user_id` at each event.
     """
     # Filter out events that have been soft failed so that we don't relay them
     # to clients.
@@ -151,7 +148,7 @@ async def filter_events_for_client(
             filter_send_to_client=filter_send_to_client,
             sender_ignored=event.sender in ignore_list,
             always_include_ids=always_include_ids,
-            retention_policy=retention_policies[room_id],
+            retention_policy=retention_policies[event.room_id],
             state=state_after_event,
             is_peeking=is_peeking,
             sender_erased=erased_senders.get(event.sender, False),
@@ -159,9 +156,6 @@ async def filter_events_for_client(
         if filtered is None:
             return None
 
-        if not msc4115_membership_on_events:
-            return filtered
-
         # Annotate the event with the user's membership after the event.
         #
         # Normally we just look in `state_after_event`, but if the event is an outlier
@@ -186,7 +180,7 @@ async def filter_events_for_client(
         # Copy the event before updating the unsigned data: this shouldn't be persisted
         # to the cache!
         cloned = clone_event(filtered)
-        cloned.unsigned[EventUnsignedContentFields.MSC4115_MEMBERSHIP] = user_membership
+        cloned.unsigned[EventUnsignedContentFields.MEMBERSHIP] = user_membership
 
         return cloned
 
diff --git a/tests/events/test_utils.py b/tests/events/test_utils.py
index d5ac66a6ed..30f8787758 100644
--- a/tests/events/test_utils.py
+++ b/tests/events/test_utils.py
@@ -625,6 +625,8 @@ class CloneEventTestCase(stdlib_unittest.TestCase):
         )
         original.internal_metadata.stream_ordering = 1234
         self.assertEqual(original.internal_metadata.stream_ordering, 1234)
+        original.internal_metadata.instance_name = "worker1"
+        self.assertEqual(original.internal_metadata.instance_name, "worker1")
 
         cloned = clone_event(original)
         cloned.unsigned["b"] = 3
@@ -632,6 +634,7 @@ class CloneEventTestCase(stdlib_unittest.TestCase):
         self.assertEqual(original.unsigned, {"a": 1, "b": 2})
         self.assertEqual(cloned.unsigned, {"a": 1, "b": 3})
         self.assertEqual(cloned.internal_metadata.stream_ordering, 1234)
+        self.assertEqual(cloned.internal_metadata.instance_name, "worker1")
         self.assertEqual(cloned.internal_metadata.txn_id, "txn")
 
 
diff --git a/tests/federation/test_federation_media.py b/tests/federation/test_federation_media.py
new file mode 100644
index 0000000000..1c89d19e99
--- /dev/null
+++ b/tests/federation/test_federation_media.py
@@ -0,0 +1,234 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2024 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# Originally licensed under the Apache License, Version 2.0:
+# <http://www.apache.org/licenses/LICENSE-2.0>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+import io
+import os
+import shutil
+import tempfile
+from typing import Optional
+
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.media._base import FileInfo, Responder
+from synapse.media.filepath import MediaFilePaths
+from synapse.media.media_storage import MediaStorage
+from synapse.media.storage_provider import (
+    FileStorageProviderBackend,
+    StorageProviderWrapper,
+)
+from synapse.server import HomeServer
+from synapse.storage.databases.main.media_repository import LocalMedia
+from synapse.types import JsonDict, UserID
+from synapse.util import Clock
+
+from tests import unittest
+from tests.test_utils import SMALL_PNG
+from tests.unittest import override_config
+
+
+class FederationUnstableMediaDownloadsTest(unittest.FederatingHomeserverTestCase):
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        super().prepare(reactor, clock, hs)
+        self.test_dir = tempfile.mkdtemp(prefix="synapse-tests-")
+        self.addCleanup(shutil.rmtree, self.test_dir)
+        self.primary_base_path = os.path.join(self.test_dir, "primary")
+        self.secondary_base_path = os.path.join(self.test_dir, "secondary")
+
+        hs.config.media.media_store_path = self.primary_base_path
+
+        storage_providers = [
+            StorageProviderWrapper(
+                FileStorageProviderBackend(hs, self.secondary_base_path),
+                store_local=True,
+                store_remote=False,
+                store_synchronous=True,
+            )
+        ]
+
+        self.filepaths = MediaFilePaths(self.primary_base_path)
+        self.media_storage = MediaStorage(
+            hs, self.primary_base_path, self.filepaths, storage_providers
+        )
+        self.media_repo = hs.get_media_repository()
+
+    @override_config(
+        {"experimental_features": {"msc3916_authenticated_media_enabled": True}}
+    )
+    def test_file_download(self) -> None:
+        content = io.BytesIO(b"file_to_stream")
+        content_uri = self.get_success(
+            self.media_repo.create_content(
+                "text/plain",
+                "test_upload",
+                content,
+                46,
+                UserID.from_string("@user_id:whatever.org"),
+            )
+        )
+        # test with a text file
+        channel = self.make_signed_federation_request(
+            "GET",
+            f"/_matrix/federation/unstable/org.matrix.msc3916/media/download/{content_uri.media_id}",
+        )
+        self.pump()
+        self.assertEqual(200, channel.code)
+
+        content_type = channel.headers.getRawHeaders("content-type")
+        assert content_type is not None
+        assert "multipart/mixed" in content_type[0]
+        assert "boundary" in content_type[0]
+
+        # extract boundary
+        boundary = content_type[0].split("boundary=")[1]
+        # split on boundary and check that json field and expected value exist
+        stripped = channel.text_body.split("\r\n" + "--" + boundary)
+        # TODO: the json object expected will change once MSC3911 is implemented, currently
+        # {} is returned for all requests as a placeholder (per MSC3196)
+        found_json = any(
+            "\r\nContent-Type: application/json\r\n{}" in field for field in stripped
+        )
+        self.assertTrue(found_json)
+
+        # check that text file and expected value exist
+        found_file = any(
+            "\r\nContent-Type: text/plain\r\nfile_to_stream" in field
+            for field in stripped
+        )
+        self.assertTrue(found_file)
+
+        content = io.BytesIO(SMALL_PNG)
+        content_uri = self.get_success(
+            self.media_repo.create_content(
+                "image/png",
+                "test_png_upload",
+                content,
+                67,
+                UserID.from_string("@user_id:whatever.org"),
+            )
+        )
+        # test with an image file
+        channel = self.make_signed_federation_request(
+            "GET",
+            f"/_matrix/federation/unstable/org.matrix.msc3916/media/download/{content_uri.media_id}",
+        )
+        self.pump()
+        self.assertEqual(200, channel.code)
+
+        content_type = channel.headers.getRawHeaders("content-type")
+        assert content_type is not None
+        assert "multipart/mixed" in content_type[0]
+        assert "boundary" in content_type[0]
+
+        # extract boundary
+        boundary = content_type[0].split("boundary=")[1]
+        # split on boundary and check that json field and expected value exist
+        body = channel.result.get("body")
+        assert body is not None
+        stripped_bytes = body.split(b"\r\n" + b"--" + boundary.encode("utf-8"))
+        found_json = any(
+            b"\r\nContent-Type: application/json\r\n{}" in field
+            for field in stripped_bytes
+        )
+        self.assertTrue(found_json)
+
+        # check that png file exists and matches what was uploaded
+        found_file = any(SMALL_PNG in field for field in stripped_bytes)
+        self.assertTrue(found_file)
+
+    @override_config(
+        {"experimental_features": {"msc3916_authenticated_media_enabled": False}}
+    )
+    def test_disable_config(self) -> None:
+        content = io.BytesIO(b"file_to_stream")
+        content_uri = self.get_success(
+            self.media_repo.create_content(
+                "text/plain",
+                "test_upload",
+                content,
+                46,
+                UserID.from_string("@user_id:whatever.org"),
+            )
+        )
+        channel = self.make_signed_federation_request(
+            "GET",
+            f"/_matrix/federation/unstable/org.matrix.msc3916/media/download/{content_uri.media_id}",
+        )
+        self.pump()
+        self.assertEqual(404, channel.code)
+        self.assertEqual(channel.json_body.get("errcode"), "M_UNRECOGNIZED")
+
+
+class FakeFileStorageProviderBackend:
+    """
+    Fake storage provider stub with incompatible `fetch` signature for testing
+    """
+
+    def __init__(self, hs: "HomeServer", config: str):
+        self.hs = hs
+        self.cache_directory = hs.config.media.media_store_path
+        self.base_directory = config
+
+    def __str__(self) -> str:
+        return "FakeFileStorageProviderBackend[%s]" % (self.base_directory,)
+
+    async def fetch(
+        self, path: str, file_info: FileInfo, media_info: Optional[LocalMedia] = None
+    ) -> Optional[Responder]:
+        pass
+
+
+TEST_DIR = tempfile.mkdtemp(prefix="synapse-tests-")
+
+
+class FederationUnstableMediaEndpointCompatibilityTest(
+    unittest.FederatingHomeserverTestCase
+):
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        super().prepare(reactor, clock, hs)
+        self.test_dir = TEST_DIR
+        self.addCleanup(shutil.rmtree, self.test_dir)
+        self.media_repo = hs.get_media_repository()
+
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+        primary_base_path = os.path.join(TEST_DIR, "primary")
+        config["media_storage_providers"] = [
+            {
+                "module": "tests.federation.test_federation_media.FakeFileStorageProviderBackend",
+                "store_local": "True",
+                "store_remote": "False",
+                "store_synchronous": "False",
+                "config": {"directory": primary_base_path},
+            }
+        ]
+        return config
+
+    @override_config(
+        {"experimental_features": {"msc3916_authenticated_media_enabled": True}}
+    )
+    def test_incompatible_storage_provider_fails_to_load_endpoint(self) -> None:
+        channel = self.make_signed_federation_request(
+            "GET",
+            "/_matrix/federation/unstable/org.matrix.msc3916/media/download/xyz",
+        )
+        self.pump()
+        self.assertEqual(404, channel.code)
+        self.assertEqual(channel.json_body.get("errcode"), "M_UNRECOGNIZED")
diff --git a/tests/handlers/test_oauth_delegation.py b/tests/handlers/test_oauth_delegation.py
index 9387d07de8..036c539db2 100644
--- a/tests/handlers/test_oauth_delegation.py
+++ b/tests/handlers/test_oauth_delegation.py
@@ -541,6 +541,8 @@ class MSC3861OAuthDelegation(HomeserverTestCase):
 
         self.assertEqual(channel.code, 200, channel.json_body)
 
+        # Try uploading *different* keys; it should cause a 501 error.
+        keys_upload_body = self.make_device_keys(USER_ID, DEVICE)
         channel = self.make_request(
             "POST",
             "/_matrix/client/v3/keys/device_signing/upload",
diff --git a/tests/handlers/test_sliding_sync.py b/tests/handlers/test_sliding_sync.py
new file mode 100644
index 0000000000..0358239c7f
--- /dev/null
+++ b/tests/handlers/test_sliding_sync.py
@@ -0,0 +1,1476 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2024 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+# Originally licensed under the Apache License, Version 2.0:
+# <http://www.apache.org/licenses/LICENSE-2.0>.
+#
+# [This file includes modifications made by New Vector Limited]
+#
+#
+import logging
+from unittest.mock import patch
+
+from parameterized import parameterized
+
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.api.constants import AccountDataTypes, EventTypes, JoinRules, Membership
+from synapse.api.room_versions import RoomVersions
+from synapse.handlers.sliding_sync import SlidingSyncConfig
+from synapse.rest import admin
+from synapse.rest.client import knock, login, room
+from synapse.server import HomeServer
+from synapse.storage.util.id_generators import MultiWriterIdGenerator
+from synapse.types import JsonDict, UserID
+from synapse.util import Clock
+
+from tests.replication._base import BaseMultiWorkerStreamTestCase
+from tests.unittest import HomeserverTestCase
+
+logger = logging.getLogger(__name__)
+
+
+class GetSyncRoomIdsForUserTestCase(HomeserverTestCase):
+    """
+    Tests Sliding Sync handler `get_sync_room_ids_for_user()` to make sure it returns
+    the correct list of rooms IDs.
+    """
+
+    servlets = [
+        admin.register_servlets,
+        knock.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+        # Enable sliding sync
+        config["experimental_features"] = {"msc3575_enabled": True}
+        return config
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.sliding_sync_handler = self.hs.get_sliding_sync_handler()
+        self.store = self.hs.get_datastores().main
+        self.event_sources = hs.get_event_sources()
+
+    def test_no_rooms(self) -> None:
+        """
+        Test when the user has never joined any rooms before
+        """
+        user1_id = self.register_user("user1", "pass")
+        # user1_tok = self.login(user1_id, "pass")
+
+        now_token = self.event_sources.get_current_token()
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=now_token,
+                to_token=now_token,
+            )
+        )
+
+        self.assertEqual(room_id_results.keys(), set())
+
+    def test_get_newly_joined_room(self) -> None:
+        """
+        Test that rooms that the user has newly_joined show up. newly_joined is when you
+        join after the `from_token` and <= `to_token`.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        before_room_token = self.event_sources.get_current_token()
+
+        room_id = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+
+        after_room_token = self.event_sources.get_current_token()
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room_token,
+                to_token=after_room_token,
+            )
+        )
+
+        self.assertEqual(room_id_results.keys(), {room_id})
+
+    def test_get_already_joined_room(self) -> None:
+        """
+        Test that rooms that the user is already joined show up.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+
+        after_room_token = self.event_sources.get_current_token()
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_room_token,
+                to_token=after_room_token,
+            )
+        )
+
+        self.assertEqual(room_id_results.keys(), {room_id})
+
+    def test_get_invited_banned_knocked_room(self) -> None:
+        """
+        Test that rooms that the user is invited to, banned from, and knocked on show
+        up.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        before_room_token = self.event_sources.get_current_token()
+
+        # Setup the invited room (user2 invites user1 to the room)
+        invited_room_id = self.helper.create_room_as(user2_id, tok=user2_tok)
+        self.helper.invite(invited_room_id, targ=user1_id, tok=user2_tok)
+
+        # Setup the ban room (user2 bans user1 from the room)
+        ban_room_id = self.helper.create_room_as(
+            user2_id, tok=user2_tok, is_public=True
+        )
+        self.helper.join(ban_room_id, user1_id, tok=user1_tok)
+        self.helper.ban(ban_room_id, src=user2_id, targ=user1_id, tok=user2_tok)
+
+        # Setup the knock room (user1 knocks on the room)
+        knock_room_id = self.helper.create_room_as(
+            user2_id, tok=user2_tok, room_version=RoomVersions.V7.identifier
+        )
+        self.helper.send_state(
+            knock_room_id,
+            EventTypes.JoinRules,
+            {"join_rule": JoinRules.KNOCK},
+            tok=user2_tok,
+        )
+        # User1 knocks on the room
+        channel = self.make_request(
+            "POST",
+            "/_matrix/client/r0/knock/%s" % (knock_room_id,),
+            b"{}",
+            user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+
+        after_room_token = self.event_sources.get_current_token()
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room_token,
+                to_token=after_room_token,
+            )
+        )
+
+        # Ensure that the invited, ban, and knock rooms show up
+        self.assertEqual(
+            room_id_results.keys(),
+            {
+                invited_room_id,
+                ban_room_id,
+                knock_room_id,
+            },
+        )
+
+    def test_get_kicked_room(self) -> None:
+        """
+        Test that a room that the user was kicked from still shows up. When the user
+        comes back to their client, they should see that they were kicked.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # Setup the kick room (user2 kicks user1 from the room)
+        kick_room_id = self.helper.create_room_as(
+            user2_id, tok=user2_tok, is_public=True
+        )
+        self.helper.join(kick_room_id, user1_id, tok=user1_tok)
+        # Kick user1 from the room
+        self.helper.change_membership(
+            room=kick_room_id,
+            src=user2_id,
+            targ=user1_id,
+            tok=user2_tok,
+            membership=Membership.LEAVE,
+            extra_data={
+                "reason": "Bad manners",
+            },
+        )
+
+        after_kick_token = self.event_sources.get_current_token()
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_kick_token,
+                to_token=after_kick_token,
+            )
+        )
+
+        # The kicked room should show up
+        self.assertEqual(room_id_results.keys(), {kick_room_id})
+
+    def test_forgotten_rooms(self) -> None:
+        """
+        Forgotten rooms do not show up even if we forget after the from/to range.
+
+        Ideally, we would be able to track when the `/forget` happens and apply it
+        accordingly in the token range but the forgotten flag is only an extra bool in
+        the `room_memberships` table.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # Setup a normal room that we leave. This won't show up in the sync response
+        # because we left it before our token but is good to check anyway.
+        leave_room_id = self.helper.create_room_as(
+            user2_id, tok=user2_tok, is_public=True
+        )
+        self.helper.join(leave_room_id, user1_id, tok=user1_tok)
+        self.helper.leave(leave_room_id, user1_id, tok=user1_tok)
+
+        # Setup the ban room (user2 bans user1 from the room)
+        ban_room_id = self.helper.create_room_as(
+            user2_id, tok=user2_tok, is_public=True
+        )
+        self.helper.join(ban_room_id, user1_id, tok=user1_tok)
+        self.helper.ban(ban_room_id, src=user2_id, targ=user1_id, tok=user2_tok)
+
+        # Setup the kick room (user2 kicks user1 from the room)
+        kick_room_id = self.helper.create_room_as(
+            user2_id, tok=user2_tok, is_public=True
+        )
+        self.helper.join(kick_room_id, user1_id, tok=user1_tok)
+        # Kick user1 from the room
+        self.helper.change_membership(
+            room=kick_room_id,
+            src=user2_id,
+            targ=user1_id,
+            tok=user2_tok,
+            membership=Membership.LEAVE,
+            extra_data={
+                "reason": "Bad manners",
+            },
+        )
+
+        before_room_forgets = self.event_sources.get_current_token()
+
+        # Forget the room after we already have our tokens. This doesn't change
+        # the membership event itself but will mark it internally in Synapse
+        channel = self.make_request(
+            "POST",
+            f"/_matrix/client/r0/rooms/{leave_room_id}/forget",
+            content={},
+            access_token=user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+        channel = self.make_request(
+            "POST",
+            f"/_matrix/client/r0/rooms/{ban_room_id}/forget",
+            content={},
+            access_token=user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+        channel = self.make_request(
+            "POST",
+            f"/_matrix/client/r0/rooms/{kick_room_id}/forget",
+            content={},
+            access_token=user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room_forgets,
+                to_token=before_room_forgets,
+            )
+        )
+
+        # We shouldn't see the room because it was forgotten
+        self.assertEqual(room_id_results.keys(), set())
+
+    def test_only_newly_left_rooms_show_up(self) -> None:
+        """
+        Test that newly_left rooms still show up in the sync response but rooms that
+        were left before the `from_token` don't show up. See condition "2)" comments in
+        the `get_sync_room_ids_for_user` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Leave before we calculate the `from_token`
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Leave during the from_token/to_token range (newly_left)
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        self.helper.leave(room_id2, user1_id, tok=user1_tok)
+
+        after_room2_token = self.event_sources.get_current_token()
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_room1_token,
+                to_token=after_room2_token,
+            )
+        )
+
+        # Only the newly_left room should show up
+        self.assertEqual(room_id_results.keys(), {room_id2})
+
+    def test_no_joins_after_to_token(self) -> None:
+        """
+        Rooms we join after the `to_token` should *not* show up. See condition "1b)"
+        comments in the `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        before_room1_token = self.event_sources.get_current_token()
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Room join after after our `to_token` shouldn't show up
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok)
+        _ = room_id2
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_join_during_range_and_left_room_after_to_token(self) -> None:
+        """
+        Room still shows up if we left the room but were joined during the
+        from_token/to_token. See condition "1a)" comments in the
+        `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        before_room1_token = self.event_sources.get_current_token()
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Leave the room after we already have our tokens
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # We should still see the room because we were joined during the
+        # from_token/to_token time period.
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_join_before_range_and_left_room_after_to_token(self) -> None:
+        """
+        Room still shows up if we left the room but were joined before the `from_token`
+        so it should show up. See condition "1a)" comments in the
+        `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Leave the room after we already have our tokens
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # We should still see the room because we were joined before the `from_token`
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_kicked_before_range_and_left_after_to_token(self) -> None:
+        """
+        Room still shows up if we left the room but were kicked before the `from_token`
+        so it should show up. See condition "1a)" comments in the
+        `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # Setup the kick room (user2 kicks user1 from the room)
+        kick_room_id = self.helper.create_room_as(
+            user2_id, tok=user2_tok, is_public=True
+        )
+        self.helper.join(kick_room_id, user1_id, tok=user1_tok)
+        # Kick user1 from the room
+        self.helper.change_membership(
+            room=kick_room_id,
+            src=user2_id,
+            targ=user1_id,
+            tok=user2_tok,
+            membership=Membership.LEAVE,
+            extra_data={
+                "reason": "Bad manners",
+            },
+        )
+
+        after_kick_token = self.event_sources.get_current_token()
+
+        # Leave the room after we already have our tokens
+        #
+        # We have to join before we can leave (leave -> leave isn't a valid transition
+        # or at least it doesn't work in Synapse, 403 forbidden)
+        self.helper.join(kick_room_id, user1_id, tok=user1_tok)
+        self.helper.leave(kick_room_id, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_kick_token,
+                to_token=after_kick_token,
+            )
+        )
+
+        # We shouldn't see the room because it was forgotten
+        self.assertEqual(room_id_results.keys(), {kick_room_id})
+
+    def test_newly_left_during_range_and_join_leave_after_to_token(self) -> None:
+        """
+        Newly left room should show up. But we're also testing that joining and leaving
+        after the `to_token` doesn't mess with the results. See condition "2)" and "1a)"
+        comments in the `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        before_room1_token = self.event_sources.get_current_token()
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # Join and leave the room during the from/to range
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Join and leave the room after we already have our tokens
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # Room should still show up because it's newly_left during the from/to range
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_newly_left_during_range_and_join_after_to_token(self) -> None:
+        """
+        Newly left room should show up. But we're also testing that joining after the
+        `to_token` doesn't mess with the results. See condition "2)" and "1b)" comments
+        in the `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        before_room1_token = self.event_sources.get_current_token()
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # Join and leave the room during the from/to range
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Join the room after we already have our tokens
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # Room should still show up because it's newly_left during the from/to range
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_no_from_token(self) -> None:
+        """
+        Test that if we don't provide a `from_token`, we get all the rooms that we we're
+        joined to up to the `to_token`.
+
+        Providing `from_token` only really has the effect that it adds `newly_left`
+        rooms to the response.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        room_id2 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+
+        # Join room1
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+
+        # Join and leave the room2 before the `to_token`
+        self.helper.join(room_id2, user1_id, tok=user1_tok)
+        self.helper.leave(room_id2, user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Join the room2 after we already have our tokens
+        self.helper.join(room_id2, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=None,
+                to_token=after_room1_token,
+            )
+        )
+
+        # Only rooms we were joined to before the `to_token` should show up
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_from_token_ahead_of_to_token(self) -> None:
+        """
+        Test when the provided `from_token` comes after the `to_token`. We should
+        basically expect the same result as having no `from_token`.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        room_id2 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        room_id3 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        room_id4 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+
+        # Join room1 before `before_room_token`
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+
+        # Join and leave the room2 before `before_room_token`
+        self.helper.join(room_id2, user1_id, tok=user1_tok)
+        self.helper.leave(room_id2, user1_id, tok=user1_tok)
+
+        # Note: These are purposely swapped. The `from_token` should come after
+        # the `to_token` in this test
+        to_token = self.event_sources.get_current_token()
+
+        # Join room2 after `before_room_token`
+        self.helper.join(room_id2, user1_id, tok=user1_tok)
+
+        # --------
+
+        # Join room3 after `before_room_token`
+        self.helper.join(room_id3, user1_id, tok=user1_tok)
+
+        # Join and leave the room4 after `before_room_token`
+        self.helper.join(room_id4, user1_id, tok=user1_tok)
+        self.helper.leave(room_id4, user1_id, tok=user1_tok)
+
+        # Note: These are purposely swapped. The `from_token` should come after the
+        # `to_token` in this test
+        from_token = self.event_sources.get_current_token()
+
+        # Join the room4 after we already have our tokens
+        self.helper.join(room_id4, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=from_token,
+                to_token=to_token,
+            )
+        )
+
+        # Only rooms we were joined to before the `to_token` should show up
+        #
+        # There won't be any newly_left rooms because the `from_token` is ahead of the
+        # `to_token` and that range will give no membership changes to check.
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_leave_before_range_and_join_leave_after_to_token(self) -> None:
+        """
+        Old left room shouldn't show up. But we're also testing that joining and leaving
+        after the `to_token` doesn't mess with the results. See condition "1a)" comments
+        in the `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # Join and leave the room before the from/to range
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Join and leave the room after we already have our tokens
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # Room shouldn't show up because it was left before the `from_token`
+        self.assertEqual(room_id_results.keys(), set())
+
+    def test_leave_before_range_and_join_after_to_token(self) -> None:
+        """
+        Old left room shouldn't show up. But we're also testing that joining after the
+        `to_token` doesn't mess with the results. See condition "1b)" comments in the
+        `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # Join and leave the room before the from/to range
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Join the room after we already have our tokens
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # Room shouldn't show up because it was left before the `from_token`
+        self.assertEqual(room_id_results.keys(), set())
+
+    def test_join_leave_multiple_times_during_range_and_after_to_token(
+        self,
+    ) -> None:
+        """
+        Join and leave multiple times shouldn't affect rooms from showing up. It just
+        matters that we were joined or newly_left in the from/to range. But we're also
+        testing that joining and leaving after the `to_token` doesn't mess with the
+        results.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        before_room1_token = self.event_sources.get_current_token()
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # Join, leave, join back to the room before the from/to range
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Leave and Join the room multiple times after we already have our tokens
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # Room should show up because it was newly_left and joined during the from/to range
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_join_leave_multiple_times_before_range_and_after_to_token(
+        self,
+    ) -> None:
+        """
+        Join and leave multiple times before the from/to range shouldn't affect rooms
+        from showing up. It just matters that we were joined or newly_left in the
+        from/to range. But we're also testing that joining and leaving after the
+        `to_token` doesn't mess with the results.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # Join, leave, join back to the room before the from/to range
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Leave and Join the room multiple times after we already have our tokens
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # Room should show up because we were joined before the from/to range
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_invite_before_range_and_join_leave_after_to_token(
+        self,
+    ) -> None:
+        """
+        Make it look like we joined after the token range but we were invited before the
+        from/to range so the room should still show up. See condition "1a)" comments in
+        the `get_sync_room_ids_for_user()` method.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+
+        # Invited to the room before the token
+        self.helper.invite(room_id1, src=user2_id, targ=user1_id, tok=user2_tok)
+
+        after_room1_token = self.event_sources.get_current_token()
+
+        # Join and leave the room after we already have our tokens
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=after_room1_token,
+                to_token=after_room1_token,
+            )
+        )
+
+        # Room should show up because we were invited before the from/to range
+        self.assertEqual(room_id_results.keys(), {room_id1})
+
+    def test_multiple_rooms_are_not_confused(
+        self,
+    ) -> None:
+        """
+        Test that multiple rooms are not confused as we fixup the list. This test is
+        spawning from a real world bug in the code where I was accidentally using
+        `event.room_id` in one of the fix-up loops but the `event` being referenced was
+        actually from a different loop.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # We create the room with user2 so the room isn't left with no members when we
+        # leave and can still re-join.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        room_id2 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+
+        # Invited and left the room before the token
+        self.helper.invite(room_id1, src=user2_id, targ=user1_id, tok=user2_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+        # Invited to room2
+        self.helper.invite(room_id2, src=user2_id, targ=user1_id, tok=user2_tok)
+
+        before_room3_token = self.event_sources.get_current_token()
+
+        # Invited and left room3 during the from/to range
+        room_id3 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        self.helper.invite(room_id3, src=user2_id, targ=user1_id, tok=user2_tok)
+        self.helper.leave(room_id3, user1_id, tok=user1_tok)
+
+        after_room3_token = self.event_sources.get_current_token()
+
+        # Join and leave the room after we already have our tokens
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+        # Leave room2
+        self.helper.leave(room_id2, user1_id, tok=user1_tok)
+        # Leave room3
+        self.helper.leave(room_id3, user1_id, tok=user1_tok)
+
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_room3_token,
+                to_token=after_room3_token,
+            )
+        )
+
+        self.assertEqual(
+            room_id_results.keys(),
+            {
+                # `room_id1` shouldn't show up because we left before the from/to range
+                #
+                # Room should show up because we were invited before the from/to range
+                room_id2,
+                # Room should show up because it was newly_left during the from/to range
+                room_id3,
+            },
+        )
+
+
+class GetSyncRoomIdsForUserEventShardTestCase(BaseMultiWorkerStreamTestCase):
+    """
+    Tests Sliding Sync handler `get_sync_room_ids_for_user()` to make sure it works with
+    sharded event stream_writers enabled
+    """
+
+    servlets = [
+        admin.register_servlets_for_client_rest_resource,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def default_config(self) -> dict:
+        config = super().default_config()
+        # Enable sliding sync
+        config["experimental_features"] = {"msc3575_enabled": True}
+
+        # Enable shared event stream_writers
+        config["stream_writers"] = {"events": ["worker1", "worker2", "worker3"]}
+        config["instance_map"] = {
+            "main": {"host": "testserv", "port": 8765},
+            "worker1": {"host": "testserv", "port": 1001},
+            "worker2": {"host": "testserv", "port": 1002},
+            "worker3": {"host": "testserv", "port": 1003},
+        }
+        return config
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.sliding_sync_handler = self.hs.get_sliding_sync_handler()
+        self.store = self.hs.get_datastores().main
+        self.event_sources = hs.get_event_sources()
+
+    def _create_room(self, room_id: str, user_id: str, tok: str) -> None:
+        """
+        Create a room with a specific room_id. We use this so that that we have a
+        consistent room_id across test runs that hashes to the same value and will be
+        sharded to a known worker in the tests.
+        """
+
+        # We control the room ID generation by patching out the
+        # `_generate_room_id` method
+        with patch(
+            "synapse.handlers.room.RoomCreationHandler._generate_room_id"
+        ) as mock:
+            mock.side_effect = lambda: room_id
+            self.helper.create_room_as(user_id, tok=tok)
+
+    def test_sharded_event_persisters(self) -> None:
+        """
+        This test should catch bugs that would come from flawed stream position
+        (`stream_ordering`) comparisons or making `RoomStreamToken`'s naively. To
+        compare event positions properly, you need to consider both the `instance_name`
+        and `stream_ordering` together.
+
+        The test creates three event persister workers and a room that is sharded to
+        each worker. On worker2, we make the event stream position stuck so that it lags
+        behind the other workers and we start getting `RoomStreamToken` that have an
+        `instance_map` component (i.e. q`m{min_pos}~{writer1}.{pos1}~{writer2}.{pos2}`).
+
+        We then send some events to advance the stream positions of worker1 and worker3
+        but worker2 is lagging behind because it's stuck. We are specifically testing
+        that `get_sync_room_ids_for_user(from_token=xxx, to_token=xxx)` should work
+        correctly in these adverse conditions.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        self.make_worker_hs(
+            "synapse.app.generic_worker",
+            {"worker_name": "worker1"},
+        )
+
+        worker_hs2 = self.make_worker_hs(
+            "synapse.app.generic_worker",
+            {"worker_name": "worker2"},
+        )
+
+        self.make_worker_hs(
+            "synapse.app.generic_worker",
+            {"worker_name": "worker3"},
+        )
+
+        # Specially crafted room IDs that get persisted on different workers.
+        #
+        # Sharded to worker1
+        room_id1 = "!fooo:test"
+        # Sharded to worker2
+        room_id2 = "!bar:test"
+        # Sharded to worker3
+        room_id3 = "!quux:test"
+
+        # Create rooms on the different workers.
+        self._create_room(room_id1, user2_id, user2_tok)
+        self._create_room(room_id2, user2_id, user2_tok)
+        self._create_room(room_id3, user2_id, user2_tok)
+        join_response1 = self.helper.join(room_id1, user1_id, tok=user1_tok)
+        join_response2 = self.helper.join(room_id2, user1_id, tok=user1_tok)
+        # Leave room2
+        self.helper.leave(room_id2, user1_id, tok=user1_tok)
+        join_response3 = self.helper.join(room_id3, user1_id, tok=user1_tok)
+        # Leave room3
+        self.helper.leave(room_id3, user1_id, tok=user1_tok)
+
+        # Ensure that the events were sharded to different workers.
+        pos1 = self.get_success(
+            self.store.get_position_for_event(join_response1["event_id"])
+        )
+        self.assertEqual(pos1.instance_name, "worker1")
+        pos2 = self.get_success(
+            self.store.get_position_for_event(join_response2["event_id"])
+        )
+        self.assertEqual(pos2.instance_name, "worker2")
+        pos3 = self.get_success(
+            self.store.get_position_for_event(join_response3["event_id"])
+        )
+        self.assertEqual(pos3.instance_name, "worker3")
+
+        before_stuck_activity_token = self.event_sources.get_current_token()
+
+        # We now gut wrench into the events stream `MultiWriterIdGenerator` on worker2 to
+        # mimic it getting stuck persisting an event. This ensures that when we send an
+        # event on worker1/worker3 we end up in a state where worker2 events stream
+        # position lags that on worker1/worker3, resulting in a RoomStreamToken with a
+        # non-empty `instance_map` component.
+        #
+        # Worker2's event stream position will not advance until we call `__aexit__`
+        # again.
+        worker_store2 = worker_hs2.get_datastores().main
+        assert isinstance(worker_store2._stream_id_gen, MultiWriterIdGenerator)
+        actx = worker_store2._stream_id_gen.get_next()
+        self.get_success(actx.__aenter__())
+
+        # For room_id1/worker1: leave and join the room to advance the stream position
+        # and generate membership changes.
+        self.helper.leave(room_id1, user1_id, tok=user1_tok)
+        self.helper.join(room_id1, user1_id, tok=user1_tok)
+        # For room_id2/worker2: which is currently stuck, join the room.
+        join_on_worker2_response = self.helper.join(room_id2, user1_id, tok=user1_tok)
+        # For room_id3/worker3: leave and join the room to advance the stream position
+        # and generate membership changes.
+        self.helper.leave(room_id3, user1_id, tok=user1_tok)
+        join_on_worker3_response = self.helper.join(room_id3, user1_id, tok=user1_tok)
+
+        # Get a token while things are stuck after our activity
+        stuck_activity_token = self.event_sources.get_current_token()
+        # Let's make sure we're working with a token that has an `instance_map`
+        self.assertNotEqual(len(stuck_activity_token.room_key.instance_map), 0)
+
+        # Just double check that the join event on worker2 (that is stuck) happened
+        # after the position recorded for worker2 in the token but before the max
+        # position in the token. This is crucial for the behavior we're trying to test.
+        join_on_worker2_pos = self.get_success(
+            self.store.get_position_for_event(join_on_worker2_response["event_id"])
+        )
+        # Ensure the join technially came after our token
+        self.assertGreater(
+            join_on_worker2_pos.stream,
+            stuck_activity_token.room_key.get_stream_pos_for_instance("worker2"),
+        )
+        # But less than the max stream position of some other worker
+        self.assertLess(
+            join_on_worker2_pos.stream,
+            # max
+            stuck_activity_token.room_key.get_max_stream_pos(),
+        )
+
+        # Just double check that the join event on worker3 happened after the min stream
+        # value in the token but still within the position recorded for worker3. This is
+        # crucial for the behavior we're trying to test.
+        join_on_worker3_pos = self.get_success(
+            self.store.get_position_for_event(join_on_worker3_response["event_id"])
+        )
+        # Ensure the join came after the min but still encapsulated by the token
+        self.assertGreaterEqual(
+            join_on_worker3_pos.stream,
+            # min
+            stuck_activity_token.room_key.stream,
+        )
+        self.assertLessEqual(
+            join_on_worker3_pos.stream,
+            stuck_activity_token.room_key.get_stream_pos_for_instance("worker3"),
+        )
+
+        # We finish the fake persisting an event we started above and advance worker2's
+        # event stream position (unstuck worker2).
+        self.get_success(actx.__aexit__(None, None, None))
+
+        # The function under test
+        room_id_results = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_stuck_activity_token,
+                to_token=stuck_activity_token,
+            )
+        )
+
+        self.assertEqual(
+            room_id_results.keys(),
+            {
+                room_id1,
+                # room_id2 shouldn't show up because we left before the from/to range
+                # and the join event during the range happened while worker2 was stuck.
+                # This means that from the perspective of the master, where the
+                # `stuck_activity_token` is generated, the stream position for worker2
+                # wasn't advanced to the join yet. Looking at the `instance_map`, the
+                # join technically comes after `stuck_activity_token``.
+                #
+                # room_id2,
+                room_id3,
+            },
+        )
+
+
+class FilterRoomsTestCase(HomeserverTestCase):
+    """
+    Tests Sliding Sync handler `filter_rooms()` to make sure it includes/excludes rooms
+    correctly.
+    """
+
+    servlets = [
+        admin.register_servlets,
+        knock.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+        # Enable sliding sync
+        config["experimental_features"] = {"msc3575_enabled": True}
+        return config
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.sliding_sync_handler = self.hs.get_sliding_sync_handler()
+        self.store = self.hs.get_datastores().main
+        self.event_sources = hs.get_event_sources()
+
+    def _create_dm_room(
+        self,
+        inviter_user_id: str,
+        inviter_tok: str,
+        invitee_user_id: str,
+        invitee_tok: str,
+    ) -> str:
+        """
+        Helper to create a DM room as the "inviter" and invite the "invitee" user to the room. The
+        "invitee" user also will join the room. The `m.direct` account data will be set
+        for both users.
+        """
+
+        # Create a room and send an invite the other user
+        room_id = self.helper.create_room_as(
+            inviter_user_id,
+            is_public=False,
+            tok=inviter_tok,
+        )
+        self.helper.invite(
+            room_id,
+            src=inviter_user_id,
+            targ=invitee_user_id,
+            tok=inviter_tok,
+            extra_data={"is_direct": True},
+        )
+        # Person that was invited joins the room
+        self.helper.join(room_id, invitee_user_id, tok=invitee_tok)
+
+        # Mimic the client setting the room as a direct message in the global account
+        # data
+        self.get_success(
+            self.store.add_account_data_for_user(
+                invitee_user_id,
+                AccountDataTypes.DIRECT,
+                {inviter_user_id: [room_id]},
+            )
+        )
+        self.get_success(
+            self.store.add_account_data_for_user(
+                inviter_user_id,
+                AccountDataTypes.DIRECT,
+                {invitee_user_id: [room_id]},
+            )
+        )
+
+        return room_id
+
+    def test_filter_dm_rooms(self) -> None:
+        """
+        Test `filter.is_dm` for DM rooms
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # Create a normal room
+        room_id = self.helper.create_room_as(
+            user1_id,
+            is_public=False,
+            tok=user1_tok,
+        )
+
+        # Create a DM room
+        dm_room_id = self._create_dm_room(
+            inviter_user_id=user1_id,
+            inviter_tok=user1_tok,
+            invitee_user_id=user2_id,
+            invitee_tok=user2_tok,
+        )
+
+        after_rooms_token = self.event_sources.get_current_token()
+
+        # Get the rooms the user should be syncing with
+        sync_room_map = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=None,
+                to_token=after_rooms_token,
+            )
+        )
+
+        # Try with `is_dm=True`
+        truthy_filtered_room_map = self.get_success(
+            self.sliding_sync_handler.filter_rooms(
+                UserID.from_string(user1_id),
+                sync_room_map,
+                SlidingSyncConfig.SlidingSyncList.Filters(
+                    is_dm=True,
+                ),
+                after_rooms_token,
+            )
+        )
+
+        self.assertEqual(truthy_filtered_room_map.keys(), {dm_room_id})
+
+        # Try with `is_dm=False`
+        falsy_filtered_room_map = self.get_success(
+            self.sliding_sync_handler.filter_rooms(
+                UserID.from_string(user1_id),
+                sync_room_map,
+                SlidingSyncConfig.SlidingSyncList.Filters(
+                    is_dm=False,
+                ),
+                after_rooms_token,
+            )
+        )
+
+        self.assertEqual(falsy_filtered_room_map.keys(), {room_id})
+
+    def test_filter_encrypted_rooms(self) -> None:
+        """
+        Test `filter.is_encrypted` for encrypted rooms
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Create a normal room
+        room_id = self.helper.create_room_as(
+            user1_id,
+            is_public=False,
+            tok=user1_tok,
+        )
+
+        # Create an encrypted room
+        encrypted_room_id = self.helper.create_room_as(
+            user1_id,
+            is_public=False,
+            tok=user1_tok,
+        )
+        self.helper.send_state(
+            encrypted_room_id,
+            EventTypes.RoomEncryption,
+            {"algorithm": "m.megolm.v1.aes-sha2"},
+            tok=user1_tok,
+        )
+
+        after_rooms_token = self.event_sources.get_current_token()
+
+        # Get the rooms the user should be syncing with
+        sync_room_map = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=None,
+                to_token=after_rooms_token,
+            )
+        )
+
+        # Try with `is_encrypted=True`
+        truthy_filtered_room_map = self.get_success(
+            self.sliding_sync_handler.filter_rooms(
+                UserID.from_string(user1_id),
+                sync_room_map,
+                SlidingSyncConfig.SlidingSyncList.Filters(
+                    is_encrypted=True,
+                ),
+                after_rooms_token,
+            )
+        )
+
+        self.assertEqual(truthy_filtered_room_map.keys(), {encrypted_room_id})
+
+        # Try with `is_encrypted=False`
+        falsy_filtered_room_map = self.get_success(
+            self.sliding_sync_handler.filter_rooms(
+                UserID.from_string(user1_id),
+                sync_room_map,
+                SlidingSyncConfig.SlidingSyncList.Filters(
+                    is_encrypted=False,
+                ),
+                after_rooms_token,
+            )
+        )
+
+        self.assertEqual(falsy_filtered_room_map.keys(), {room_id})
+
+
+class SortRoomsTestCase(HomeserverTestCase):
+    """
+    Tests Sliding Sync handler `sort_rooms()` to make sure it sorts/orders rooms
+    correctly.
+    """
+
+    servlets = [
+        admin.register_servlets,
+        knock.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+        # Enable sliding sync
+        config["experimental_features"] = {"msc3575_enabled": True}
+        return config
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.sliding_sync_handler = self.hs.get_sliding_sync_handler()
+        self.store = self.hs.get_datastores().main
+        self.event_sources = hs.get_event_sources()
+
+    def test_sort_activity_basic(self) -> None:
+        """
+        Rooms with newer activity are sorted first.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(
+            user1_id,
+            tok=user1_tok,
+        )
+        room_id2 = self.helper.create_room_as(
+            user1_id,
+            tok=user1_tok,
+        )
+
+        after_rooms_token = self.event_sources.get_current_token()
+
+        # Get the rooms the user should be syncing with
+        sync_room_map = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=None,
+                to_token=after_rooms_token,
+            )
+        )
+
+        # Sort the rooms (what we're testing)
+        sorted_room_info = self.get_success(
+            self.sliding_sync_handler.sort_rooms(
+                sync_room_map=sync_room_map,
+                to_token=after_rooms_token,
+            )
+        )
+
+        self.assertEqual(
+            [room_id for room_id, _ in sorted_room_info],
+            [room_id2, room_id1],
+        )
+
+    @parameterized.expand(
+        [
+            (Membership.LEAVE,),
+            (Membership.INVITE,),
+            (Membership.KNOCK,),
+            (Membership.BAN,),
+        ]
+    )
+    def test_activity_after_xxx(self, room1_membership: str) -> None:
+        """
+        When someone has left/been invited/knocked/been banned from a room, they
+        shouldn't take anything into account after that membership event.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        before_rooms_token = self.event_sources.get_current_token()
+
+        # Create the rooms as user2 so we can have user1 with a clean slate to work from
+        # and join in whatever order we need for the tests.
+        room_id1 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # If we're testing knocks, set the room to knock
+        if room1_membership == Membership.KNOCK:
+            self.helper.send_state(
+                room_id1,
+                EventTypes.JoinRules,
+                {"join_rule": JoinRules.KNOCK},
+                tok=user2_tok,
+            )
+        room_id2 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        room_id3 = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+
+        # Here is the activity with user1 that will determine the sort of the rooms
+        # (room2, room1, room3)
+        self.helper.join(room_id3, user1_id, tok=user1_tok)
+        if room1_membership == Membership.LEAVE:
+            self.helper.join(room_id1, user1_id, tok=user1_tok)
+            self.helper.leave(room_id1, user1_id, tok=user1_tok)
+        elif room1_membership == Membership.INVITE:
+            self.helper.invite(room_id1, src=user2_id, targ=user1_id, tok=user2_tok)
+        elif room1_membership == Membership.KNOCK:
+            self.helper.knock(room_id1, user1_id, tok=user1_tok)
+        elif room1_membership == Membership.BAN:
+            self.helper.ban(room_id1, src=user2_id, targ=user1_id, tok=user2_tok)
+        self.helper.join(room_id2, user1_id, tok=user1_tok)
+
+        # Activity before the token but the user is only been xxx to this room so it
+        # shouldn't be taken into account
+        self.helper.send(room_id1, "activity in room1", tok=user2_tok)
+
+        after_rooms_token = self.event_sources.get_current_token()
+
+        # Activity after the token. Just make it in a different order than what we
+        # expect to make sure we're not taking the activity after the token into
+        # account.
+        self.helper.send(room_id1, "activity in room1", tok=user2_tok)
+        self.helper.send(room_id2, "activity in room2", tok=user2_tok)
+        self.helper.send(room_id3, "activity in room3", tok=user2_tok)
+
+        # Get the rooms the user should be syncing with
+        sync_room_map = self.get_success(
+            self.sliding_sync_handler.get_sync_room_ids_for_user(
+                UserID.from_string(user1_id),
+                from_token=before_rooms_token,
+                to_token=after_rooms_token,
+            )
+        )
+
+        # Sort the rooms (what we're testing)
+        sorted_room_info = self.get_success(
+            self.sliding_sync_handler.sort_rooms(
+                sync_room_map=sync_room_map,
+                to_token=after_rooms_token,
+            )
+        )
+
+        self.assertEqual(
+            [room_id for room_id, _ in sorted_room_info],
+            [room_id2, room_id1, room_id3],
+            "Corresponding map to disambiguate the opaque room IDs: "
+            + str(
+                {
+                    "room_id1": room_id1,
+                    "room_id2": room_id2,
+                    "room_id3": room_id3,
+                }
+            ),
+        )
diff --git a/tests/handlers/test_user_directory.py b/tests/handlers/test_user_directory.py
index 77c6cac449..878d9683b6 100644
--- a/tests/handlers/test_user_directory.py
+++ b/tests/handlers/test_user_directory.py
@@ -1061,6 +1061,45 @@ class UserDirectoryTestCase(unittest.HomeserverTestCase):
             {alice: ProfileInfo(display_name=None, avatar_url=MXC_DUMMY)},
         )
 
+    def test_search_punctuation(self) -> None:
+        """Test that you can search for a user that includes punctuation"""
+
+        searching_user = self.register_user("searcher", "password")
+        searching_user_tok = self.login("searcher", "password")
+
+        room_id = self.helper.create_room_as(
+            searching_user,
+            room_version=RoomVersions.V1.identifier,
+            tok=searching_user_tok,
+        )
+
+        # We want to test searching for users of the form e.g. "user-1", with
+        # various punctuation. We also test both where the prefix is numeric and
+        # alphanumeric, as e.g. postgres tokenises "user-1" as "user" and "-1".
+        i = 1
+        for char in ["-", ".", "_"]:
+            for use_numeric in [False, True]:
+                if use_numeric:
+                    prefix1 = f"{i}"
+                    prefix2 = f"{i+1}"
+                else:
+                    prefix1 = f"a{i}"
+                    prefix2 = f"a{i+1}"
+
+                local_user_1 = self.register_user(f"user{char}{prefix1}", "password")
+                local_user_2 = self.register_user(f"user{char}{prefix2}", "password")
+
+                self._add_user_to_room(room_id, RoomVersions.V1, local_user_1)
+                self._add_user_to_room(room_id, RoomVersions.V1, local_user_2)
+
+                results = self.get_success(
+                    self.handler.search_users(searching_user, local_user_1, 20)
+                )["results"]
+                received_user_id_ordering = [result["user_id"] for result in results]
+                self.assertSequenceEqual(received_user_id_ordering[:1], [local_user_1])
+
+                i += 2
+
 
 class TestUserDirSearchDisabled(unittest.HomeserverTestCase):
     servlets = [
diff --git a/tests/media/test_media_storage.py b/tests/media/test_media_storage.py
index 1bd51ceba2..47a89e9c66 100644
--- a/tests/media/test_media_storage.py
+++ b/tests/media/test_media_storage.py
@@ -25,7 +25,7 @@ import tempfile
 from binascii import unhexlify
 from io import BytesIO
 from typing import Any, BinaryIO, ClassVar, Dict, List, Optional, Tuple, Union
-from unittest.mock import Mock
+from unittest.mock import MagicMock, Mock, patch
 from urllib import parse
 
 import attr
@@ -37,16 +37,22 @@ from twisted.internet import defer
 from twisted.internet.defer import Deferred
 from twisted.python.failure import Failure
 from twisted.test.proto_helpers import MemoryReactor
+from twisted.web.http_headers import Headers
+from twisted.web.iweb import UNKNOWN_LENGTH, IResponse
 from twisted.web.resource import Resource
 
 from synapse.api.errors import Codes, HttpResponseException
+from synapse.api.ratelimiting import Ratelimiter
 from synapse.events import EventBase
 from synapse.http.types import QueryParams
 from synapse.logging.context import make_deferred_yieldable
 from synapse.media._base import FileInfo, ThumbnailInfo
 from synapse.media.filepath import MediaFilePaths
 from synapse.media.media_storage import MediaStorage, ReadableFileWrapper
-from synapse.media.storage_provider import FileStorageProviderBackend
+from synapse.media.storage_provider import (
+    FileStorageProviderBackend,
+    StorageProviderWrapper,
+)
 from synapse.media.thumbnailer import ThumbnailProvider
 from synapse.module_api import ModuleApi
 from synapse.module_api.callbacks.spamchecker_callbacks import load_legacy_spam_checkers
@@ -59,6 +65,7 @@ from synapse.util import Clock
 from tests import unittest
 from tests.server import FakeChannel
 from tests.test_utils import SMALL_PNG
+from tests.unittest import override_config
 from tests.utils import default_config
 
 
@@ -74,7 +81,14 @@ class MediaStorageTests(unittest.HomeserverTestCase):
 
         hs.config.media.media_store_path = self.primary_base_path
 
-        storage_providers = [FileStorageProviderBackend(hs, self.secondary_base_path)]
+        storage_providers = [
+            StorageProviderWrapper(
+                FileStorageProviderBackend(hs, self.secondary_base_path),
+                store_local=True,
+                store_remote=False,
+                store_synchronous=True,
+            )
+        ]
 
         self.filepaths = MediaFilePaths(self.primary_base_path)
         self.media_storage = MediaStorage(
@@ -251,9 +265,11 @@ class MediaRepoTests(unittest.HomeserverTestCase):
             destination: str,
             path: str,
             output_stream: BinaryIO,
+            download_ratelimiter: Ratelimiter,
+            ip_address: Any,
+            max_size: int,
             args: Optional[QueryParams] = None,
             retry_on_dns_fail: bool = True,
-            max_size: Optional[int] = None,
             ignore_backoff: bool = False,
             follow_redirects: bool = False,
         ) -> "Deferred[Tuple[int, Dict[bytes, List[bytes]]]]":
@@ -878,3 +894,218 @@ class SpamCheckerTestCase(unittest.HomeserverTestCase):
             tok=self.tok,
             expect_code=400,
         )
+
+
+class RemoteDownloadLimiterTestCase(unittest.HomeserverTestCase):
+    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
+        config = self.default_config()
+
+        self.storage_path = self.mktemp()
+        self.media_store_path = self.mktemp()
+        os.mkdir(self.storage_path)
+        os.mkdir(self.media_store_path)
+        config["media_store_path"] = self.media_store_path
+
+        provider_config = {
+            "module": "synapse.media.storage_provider.FileStorageProviderBackend",
+            "store_local": True,
+            "store_synchronous": False,
+            "store_remote": True,
+            "config": {"directory": self.storage_path},
+        }
+
+        config["media_storage_providers"] = [provider_config]
+
+        return self.setup_test_homeserver(config=config)
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.repo = hs.get_media_repository()
+        self.client = hs.get_federation_http_client()
+        self.store = hs.get_datastores().main
+
+    def create_resource_dict(self) -> Dict[str, Resource]:
+        # We need to manually set the resource tree to include media, the
+        # default only does `/_matrix/client` APIs.
+        return {"/_matrix/media": self.hs.get_media_repository_resource()}
+
+    # mock actually reading file body
+    def read_body_with_max_size_30MiB(*args: Any, **kwargs: Any) -> Deferred:
+        d: Deferred = defer.Deferred()
+        d.callback(31457280)
+        return d
+
+    def read_body_with_max_size_50MiB(*args: Any, **kwargs: Any) -> Deferred:
+        d: Deferred = defer.Deferred()
+        d.callback(52428800)
+        return d
+
+    @patch(
+        "synapse.http.matrixfederationclient.read_body_with_max_size",
+        read_body_with_max_size_30MiB,
+    )
+    def test_download_ratelimit_default(self) -> None:
+        """
+        Test remote media download ratelimiting against default configuration - 500MB bucket
+        and 87kb/second drain rate
+        """
+
+        # mock out actually sending the request, returns a 30MiB response
+        async def _send_request(*args: Any, **kwargs: Any) -> IResponse:
+            resp = MagicMock(spec=IResponse)
+            resp.code = 200
+            resp.length = 31457280
+            resp.headers = Headers({"Content-Type": ["application/octet-stream"]})
+            resp.phrase = b"OK"
+            return resp
+
+        self.client._send_request = _send_request  # type: ignore
+
+        # first request should go through
+        channel = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxyz",
+            shorthand=False,
+        )
+        assert channel.code == 200
+
+        # next 15 should go through
+        for i in range(15):
+            channel2 = self.make_request(
+                "GET",
+                f"/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxy{i}",
+                shorthand=False,
+            )
+            assert channel2.code == 200
+
+        # 17th will hit ratelimit
+        channel3 = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxyx",
+            shorthand=False,
+        )
+        assert channel3.code == 429
+
+        # however, a request from a different IP will go through
+        channel4 = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxyz",
+            shorthand=False,
+            client_ip="187.233.230.159",
+        )
+        assert channel4.code == 200
+
+        # at 87Kib/s it should take about 2 minutes for enough to drain from bucket that another
+        # 30MiB download is authorized - The last download was blocked at 503,316,480.
+        # The next download will be authorized when bucket hits 492,830,720
+        # (524,288,000 total capacity - 31,457,280 download size) so 503,316,480 - 492,830,720 ~= 10,485,760
+        # needs to drain before another download will be authorized, that will take ~=
+        # 2 minutes (10,485,760/89,088/60)
+        self.reactor.pump([2.0 * 60.0])
+
+        # enough has drained and next request goes through
+        channel5 = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxyb",
+            shorthand=False,
+        )
+        assert channel5.code == 200
+
+    @override_config(
+        {
+            "remote_media_download_per_second": "50M",
+            "remote_media_download_burst_count": "50M",
+        }
+    )
+    @patch(
+        "synapse.http.matrixfederationclient.read_body_with_max_size",
+        read_body_with_max_size_50MiB,
+    )
+    def test_download_rate_limit_config(self) -> None:
+        """
+        Test that download rate limit config options are correctly picked up and applied
+        """
+
+        async def _send_request(*args: Any, **kwargs: Any) -> IResponse:
+            resp = MagicMock(spec=IResponse)
+            resp.code = 200
+            resp.length = 52428800
+            resp.headers = Headers({"Content-Type": ["application/octet-stream"]})
+            resp.phrase = b"OK"
+            return resp
+
+        self.client._send_request = _send_request  # type: ignore
+
+        # first request should go through
+        channel = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxyz",
+            shorthand=False,
+        )
+        assert channel.code == 200
+
+        # immediate second request should fail
+        channel = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxy1",
+            shorthand=False,
+        )
+        assert channel.code == 429
+
+        # advance half a second
+        self.reactor.pump([0.5])
+
+        # request still fails
+        channel = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxy2",
+            shorthand=False,
+        )
+        assert channel.code == 429
+
+        # advance another half second
+        self.reactor.pump([0.5])
+
+        # enough has drained from bucket and request is successful
+        channel = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxy3",
+            shorthand=False,
+        )
+        assert channel.code == 200
+
+    @patch(
+        "synapse.http.matrixfederationclient.read_body_with_max_size",
+        read_body_with_max_size_30MiB,
+    )
+    def test_download_ratelimit_max_size_sub(self) -> None:
+        """
+        Test that if no content-length is provided, the default max size is applied instead
+        """
+
+        # mock out actually sending the request
+        async def _send_request(*args: Any, **kwargs: Any) -> IResponse:
+            resp = MagicMock(spec=IResponse)
+            resp.code = 200
+            resp.length = UNKNOWN_LENGTH
+            resp.headers = Headers({"Content-Type": ["application/octet-stream"]})
+            resp.phrase = b"OK"
+            return resp
+
+        self.client._send_request = _send_request  # type: ignore
+
+        # ten requests should go through using the max size (500MB/50MB)
+        for i in range(10):
+            channel2 = self.make_request(
+                "GET",
+                f"/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxy{i}",
+                shorthand=False,
+            )
+            assert channel2.code == 200
+
+        # eleventh will hit ratelimit
+        channel3 = self.make_request(
+            "GET",
+            "/_matrix/media/v3/download/remote.org/abcdefghijklmnopqrstuvwxyx",
+            shorthand=False,
+        )
+        assert channel3.code == 429
diff --git a/tests/push/test_email.py b/tests/push/test_email.py
index c927a73fa6..e0aab1c046 100644
--- a/tests/push/test_email.py
+++ b/tests/push/test_email.py
@@ -205,8 +205,24 @@ class EmailPusherTests(HomeserverTestCase):
 
         # Multipart: plain text, base 64 encoded; html, base 64 encoded
         multipart_msg = email.message_from_bytes(msg)
-        txt = multipart_msg.get_payload()[0].get_payload(decode=True).decode()
-        html = multipart_msg.get_payload()[1].get_payload(decode=True).decode()
+
+        # Extract the text (non-HTML) portion of the multipart Message,
+        # as a Message.
+        txt_message = multipart_msg.get_payload(i=0)
+        assert isinstance(txt_message, email.message.Message)
+
+        # Extract the actual bytes from the Message object, and decode them to a `str`.
+        txt_bytes = txt_message.get_payload(decode=True)
+        assert isinstance(txt_bytes, bytes)
+        txt = txt_bytes.decode()
+
+        # Do the same for the HTML portion of the multipart Message.
+        html_message = multipart_msg.get_payload(i=1)
+        assert isinstance(html_message, email.message.Message)
+        html_bytes = html_message.get_payload(decode=True)
+        assert isinstance(html_bytes, bytes)
+        html = html_bytes.decode()
+
         self.assertIn("/_synapse/client/unsubscribe", txt)
         self.assertIn("/_synapse/client/unsubscribe", html)
 
@@ -347,12 +363,17 @@ class EmailPusherTests(HomeserverTestCase):
         # That email should contain the room's avatar
         msg: bytes = args[5]
         # Multipart: plain text, base 64 encoded; html, base 64 encoded
-        html = (
-            email.message_from_bytes(msg)
-            .get_payload()[1]
-            .get_payload(decode=True)
-            .decode()
-        )
+
+        # Extract the html Message object from the Multipart Message.
+        # We need the asserts to convince mypy that this is OK.
+        html_message = email.message_from_bytes(msg).get_payload(i=1)
+        assert isinstance(html_message, email.message.Message)
+
+        # Extract the `bytes` from the html Message object, and decode to a `str`.
+        html = html_message.get_payload(decode=True)
+        assert isinstance(html, bytes)
+        html = html.decode()
+
         self.assertIn("_matrix/media/v1/thumbnail/DUMMY_MEDIA_ID", html)
 
     def test_empty_room(self) -> None:
diff --git a/tests/replication/storage/test_events.py b/tests/replication/storage/test_events.py
index 86c8f14d1b..a56f1e2d5d 100644
--- a/tests/replication/storage/test_events.py
+++ b/tests/replication/storage/test_events.py
@@ -141,6 +141,7 @@ class EventsWorkerStoreTestCase(BaseWorkerStoreTestCase):
         self.persist(type="m.room.create", key="", creator=USER_ID)
         self.check("get_invited_rooms_for_local_user", [USER_ID_2], [])
         event = self.persist(type="m.room.member", key=USER_ID_2, membership="invite")
+        assert event.internal_metadata.instance_name is not None
         assert event.internal_metadata.stream_ordering is not None
 
         self.replicate()
@@ -154,7 +155,10 @@ class EventsWorkerStoreTestCase(BaseWorkerStoreTestCase):
                     USER_ID,
                     "invite",
                     event.event_id,
-                    event.internal_metadata.stream_ordering,
+                    PersistedEventPosition(
+                        event.internal_metadata.instance_name,
+                        event.internal_metadata.stream_ordering,
+                    ),
                     RoomVersions.V1.identifier,
                 )
             ],
@@ -229,11 +233,12 @@ class EventsWorkerStoreTestCase(BaseWorkerStoreTestCase):
         j2 = self.persist(
             type="m.room.member", sender=USER_ID_2, key=USER_ID_2, membership="join"
         )
+        assert j2.internal_metadata.instance_name is not None
         assert j2.internal_metadata.stream_ordering is not None
         self.replicate()
 
         expected_pos = PersistedEventPosition(
-            "master", j2.internal_metadata.stream_ordering
+            j2.internal_metadata.instance_name, j2.internal_metadata.stream_ordering
         )
         self.check(
             "get_rooms_for_user_with_stream_ordering",
@@ -285,6 +290,7 @@ class EventsWorkerStoreTestCase(BaseWorkerStoreTestCase):
         msg, msgctx = self.build_event()
         self.get_success(self.persistance.persist_events([(j2, j2ctx), (msg, msgctx)]))
         self.replicate()
+        assert j2.internal_metadata.instance_name is not None
         assert j2.internal_metadata.stream_ordering is not None
 
         event_source = RoomEventSource(self.hs)
@@ -326,7 +332,8 @@ class EventsWorkerStoreTestCase(BaseWorkerStoreTestCase):
             # joined_rooms list.
             if membership_changes:
                 expected_pos = PersistedEventPosition(
-                    "master", j2.internal_metadata.stream_ordering
+                    j2.internal_metadata.instance_name,
+                    j2.internal_metadata.stream_ordering,
                 )
                 self.assertEqual(
                     joined_rooms,
diff --git a/tests/rest/admin/test_admin.py b/tests/rest/admin/test_admin.py
index 22106eb786..5f6f7213b3 100644
--- a/tests/rest/admin/test_admin.py
+++ b/tests/rest/admin/test_admin.py
@@ -435,10 +435,6 @@ class ExperimentalFeaturesTestCase(unittest.HomeserverTestCase):
             True,
             channel.json_body["features"]["msc3881"],
         )
-        self.assertEqual(
-            False,
-            channel.json_body["features"]["msc3967"],
-        )
 
         # test nothing blows up if you try to disable a feature that isn't already enabled
         url = f"{self.url}/{self.other_user}"
diff --git a/tests/rest/admin/test_event_reports.py b/tests/rest/admin/test_event_reports.py
index a0f978911a..feb410a11d 100644
--- a/tests/rest/admin/test_event_reports.py
+++ b/tests/rest/admin/test_event_reports.py
@@ -24,7 +24,7 @@ from twisted.test.proto_helpers import MemoryReactor
 
 import synapse.rest.admin
 from synapse.api.errors import Codes
-from synapse.rest.client import login, report_event, room
+from synapse.rest.client import login, reporting, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
 from synapse.util import Clock
@@ -37,7 +37,7 @@ class EventReportsTestCase(unittest.HomeserverTestCase):
         synapse.rest.admin.register_servlets,
         login.register_servlets,
         room.register_servlets,
-        report_event.register_servlets,
+        reporting.register_servlets,
     ]
 
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
@@ -453,7 +453,7 @@ class EventReportDetailTestCase(unittest.HomeserverTestCase):
         synapse.rest.admin.register_servlets,
         login.register_servlets,
         room.register_servlets,
-        report_event.register_servlets,
+        reporting.register_servlets,
     ]
 
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
diff --git a/tests/rest/client/test_account.py b/tests/rest/client/test_account.py
index 992421ffe2..a85ea994de 100644
--- a/tests/rest/client/test_account.py
+++ b/tests/rest/client/test_account.py
@@ -427,13 +427,23 @@ class PasswordResetTestCase(unittest.HomeserverTestCase):
         text = None
         for part in mail.walk():
             if part.get_content_type() == "text/plain":
-                text = part.get_payload(decode=True).decode("UTF-8")
+                text = part.get_payload(decode=True)
+                if text is not None:
+                    # According to the logic table in `get_payload`, we know that
+                    # the result of `get_payload` will be `bytes`, but mypy doesn't
+                    # know this and complains. Thus, we assert the type.
+                    assert isinstance(text, bytes)
+                    text = text.decode("UTF-8")
+
                 break
 
         if not text:
             self.fail("Could not find text portion of email to parse")
 
-        assert text is not None
+        # `text` must be a `str`, after being decoded and determined just above
+        # to not be `None` or an empty `str`.
+        assert isinstance(text, str)
+
         match = re.search(r"https://example.com\S+", text)
         assert match, "Could not find link in email"
 
@@ -1209,13 +1219,23 @@ class ThreepidEmailRestTestCase(unittest.HomeserverTestCase):
         text = None
         for part in mail.walk():
             if part.get_content_type() == "text/plain":
-                text = part.get_payload(decode=True).decode("UTF-8")
+                text = part.get_payload(decode=True)
+                if text is not None:
+                    # According to the logic table in `get_payload`, we know that
+                    # the result of `get_payload` will be `bytes`, but mypy doesn't
+                    # know this and complains. Thus, we assert the type.
+                    assert isinstance(text, bytes)
+                    text = text.decode("UTF-8")
+
                 break
 
         if not text:
             self.fail("Could not find text portion of email to parse")
 
-        assert text is not None
+        # `text` must be a `str`, after being decoded and determined just above
+        # to not be `None` or an empty `str`.
+        assert isinstance(text, str)
+
         match = re.search(r"https://example.com\S+", text)
         assert match, "Could not find link in email"
 
diff --git a/tests/rest/client/test_keys.py b/tests/rest/client/test_keys.py
index 5f0c005576..8bbd109092 100644
--- a/tests/rest/client/test_keys.py
+++ b/tests/rest/client/test_keys.py
@@ -155,71 +155,6 @@ class KeyQueryTestCase(unittest.HomeserverTestCase):
         }
 
     def test_device_signing_with_uia(self) -> None:
-        """Device signing key upload requires UIA."""
-        password = "wonderland"
-        device_id = "ABCDEFGHI"
-        alice_id = self.register_user("alice", password)
-        alice_token = self.login("alice", password, device_id=device_id)
-
-        content = self.make_device_keys(alice_id, device_id)
-
-        channel = self.make_request(
-            "POST",
-            "/_matrix/client/v3/keys/device_signing/upload",
-            content,
-            alice_token,
-        )
-
-        self.assertEqual(channel.code, HTTPStatus.UNAUTHORIZED, channel.result)
-        # Grab the session
-        session = channel.json_body["session"]
-        # Ensure that flows are what is expected.
-        self.assertIn({"stages": ["m.login.password"]}, channel.json_body["flows"])
-
-        # add UI auth
-        content["auth"] = {
-            "type": "m.login.password",
-            "identifier": {"type": "m.id.user", "user": alice_id},
-            "password": password,
-            "session": session,
-        }
-
-        channel = self.make_request(
-            "POST",
-            "/_matrix/client/v3/keys/device_signing/upload",
-            content,
-            alice_token,
-        )
-
-        self.assertEqual(channel.code, HTTPStatus.OK, channel.result)
-
-    @override_config({"ui_auth": {"session_timeout": "15m"}})
-    def test_device_signing_with_uia_session_timeout(self) -> None:
-        """Device signing key upload requires UIA buy passes with grace period."""
-        password = "wonderland"
-        device_id = "ABCDEFGHI"
-        alice_id = self.register_user("alice", password)
-        alice_token = self.login("alice", password, device_id=device_id)
-
-        content = self.make_device_keys(alice_id, device_id)
-
-        channel = self.make_request(
-            "POST",
-            "/_matrix/client/v3/keys/device_signing/upload",
-            content,
-            alice_token,
-        )
-
-        self.assertEqual(channel.code, HTTPStatus.OK, channel.result)
-
-    @override_config(
-        {
-            "experimental_features": {"msc3967_enabled": True},
-            "ui_auth": {"session_timeout": "15s"},
-        }
-    )
-    def test_device_signing_with_msc3967(self) -> None:
-        """Device signing key follows MSC3967 behaviour when enabled."""
         password = "wonderland"
         device_id = "ABCDEFGHI"
         alice_id = self.register_user("alice", password)
diff --git a/tests/rest/client/test_models.py b/tests/rest/client/test_models.py
index 534dd7bcf4..f8a56c80ca 100644
--- a/tests/rest/client/test_models.py
+++ b/tests/rest/client/test_models.py
@@ -24,7 +24,7 @@ from typing import TYPE_CHECKING
 from typing_extensions import Literal
 
 from synapse._pydantic_compat import HAS_PYDANTIC_V2
-from synapse.rest.client.models import EmailRequestTokenBody
+from synapse.types.rest.client import EmailRequestTokenBody
 
 if TYPE_CHECKING or HAS_PYDANTIC_V2:
     from pydantic.v1 import BaseModel, ValidationError
diff --git a/tests/rest/client/test_report_event.py b/tests/rest/client/test_reporting.py
index 5903771e52..009deb9cb0 100644
--- a/tests/rest/client/test_report_event.py
+++ b/tests/rest/client/test_reporting.py
@@ -22,7 +22,7 @@
 from twisted.test.proto_helpers import MemoryReactor
 
 import synapse.rest.admin
-from synapse.rest.client import login, report_event, room
+from synapse.rest.client import login, reporting, room
 from synapse.server import HomeServer
 from synapse.types import JsonDict
 from synapse.util import Clock
@@ -35,7 +35,7 @@ class ReportEventTestCase(unittest.HomeserverTestCase):
         synapse.rest.admin.register_servlets,
         login.register_servlets,
         room.register_servlets,
-        report_event.register_servlets,
+        reporting.register_servlets,
     ]
 
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
@@ -139,3 +139,92 @@ class ReportEventTestCase(unittest.HomeserverTestCase):
             "POST", self.report_path, data, access_token=self.other_user_tok
         )
         self.assertEqual(response_status, channel.code, msg=channel.result["body"])
+
+
+class ReportRoomTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+        reporting.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.other_user = self.register_user("user", "pass")
+        self.other_user_tok = self.login("user", "pass")
+
+        self.room_id = self.helper.create_room_as(
+            self.other_user, tok=self.other_user_tok, is_public=True
+        )
+        self.report_path = (
+            f"/_matrix/client/unstable/org.matrix.msc4151/rooms/{self.room_id}/report"
+        )
+
+    @unittest.override_config(
+        {
+            "experimental_features": {"msc4151_enabled": True},
+        }
+    )
+    def test_reason_str(self) -> None:
+        data = {"reason": "this makes me sad"}
+        self._assert_status(200, data)
+
+    @unittest.override_config(
+        {
+            "experimental_features": {"msc4151_enabled": True},
+        }
+    )
+    def test_no_reason(self) -> None:
+        data = {"not_reason": "for typechecking"}
+        self._assert_status(400, data)
+
+    @unittest.override_config(
+        {
+            "experimental_features": {"msc4151_enabled": True},
+        }
+    )
+    def test_reason_nonstring(self) -> None:
+        data = {"reason": 42}
+        self._assert_status(400, data)
+
+    @unittest.override_config(
+        {
+            "experimental_features": {"msc4151_enabled": True},
+        }
+    )
+    def test_reason_null(self) -> None:
+        data = {"reason": None}
+        self._assert_status(400, data)
+
+    @unittest.override_config(
+        {
+            "experimental_features": {"msc4151_enabled": True},
+        }
+    )
+    def test_cannot_report_nonexistent_room(self) -> None:
+        """
+        Tests that we don't accept event reports for rooms which do not exist.
+        """
+        channel = self.make_request(
+            "POST",
+            "/_matrix/client/unstable/org.matrix.msc4151/rooms/!bloop:example.org/report",
+            {"reason": "i am very sad"},
+            access_token=self.other_user_tok,
+            shorthand=False,
+        )
+        self.assertEqual(404, channel.code, msg=channel.result["body"])
+        self.assertEqual(
+            "Room does not exist",
+            channel.json_body["error"],
+            msg=channel.result["body"],
+        )
+
+    def _assert_status(self, response_status: int, data: JsonDict) -> None:
+        channel = self.make_request(
+            "POST",
+            self.report_path,
+            data,
+            access_token=self.other_user_tok,
+            shorthand=False,
+        )
+        self.assertEqual(response_status, channel.code, msg=channel.result["body"])
diff --git a/tests/rest/client/test_retention.py b/tests/rest/client/test_retention.py
index ceae40498e..1e5a1b0a4d 100644
--- a/tests/rest/client/test_retention.py
+++ b/tests/rest/client/test_retention.py
@@ -167,7 +167,6 @@ class RetentionTestCase(unittest.HomeserverTestCase):
                 storage_controllers,
                 self.user_id,
                 events,
-                msc4115_membership_on_events=True,
             )
         )
 
diff --git a/tests/rest/client/test_sync.py b/tests/rest/client/test_sync.py
index daeb1d3ddd..2b06767b8a 100644
--- a/tests/rest/client/test_sync.py
+++ b/tests/rest/client/test_sync.py
@@ -27,6 +27,7 @@ from twisted.test.proto_helpers import MemoryReactor
 
 import synapse.rest.admin
 from synapse.api.constants import (
+    AccountDataTypes,
     EventContentFields,
     EventTypes,
     ReceiptTypes,
@@ -34,7 +35,7 @@ from synapse.api.constants import (
 )
 from synapse.rest.client import devices, knock, login, read_marker, receipts, room, sync
 from synapse.server import HomeServer
-from synapse.types import JsonDict
+from synapse.types import JsonDict, RoomStreamToken, StreamKeyType
 from synapse.util import Clock
 
 from tests import unittest
@@ -1204,3 +1205,314 @@ class ExcludeRoomTestCase(unittest.HomeserverTestCase):
 
         self.assertNotIn(self.excluded_room_id, channel.json_body["rooms"]["join"])
         self.assertIn(self.included_room_id, channel.json_body["rooms"]["join"])
+
+
+class SlidingSyncTestCase(unittest.HomeserverTestCase):
+    """
+    Tests regarding MSC3575 Sliding Sync `/sync` endpoint.
+    """
+
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+        sync.register_servlets,
+        devices.register_servlets,
+    ]
+
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+        # Enable sliding sync
+        config["experimental_features"] = {"msc3575_enabled": True}
+        return config
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.store = hs.get_datastores().main
+        self.sync_endpoint = "/_matrix/client/unstable/org.matrix.msc3575/sync"
+        self.store = hs.get_datastores().main
+        self.event_sources = hs.get_event_sources()
+
+    def _create_dm_room(
+        self,
+        inviter_user_id: str,
+        inviter_tok: str,
+        invitee_user_id: str,
+        invitee_tok: str,
+    ) -> str:
+        """
+        Helper to create a DM room as the "inviter" and invite the "invitee" user to the
+        room. The "invitee" user also will join the room. The `m.direct` account data
+        will be set for both users.
+        """
+
+        # Create a room and send an invite the other user
+        room_id = self.helper.create_room_as(
+            inviter_user_id,
+            is_public=False,
+            tok=inviter_tok,
+        )
+        self.helper.invite(
+            room_id,
+            src=inviter_user_id,
+            targ=invitee_user_id,
+            tok=inviter_tok,
+            extra_data={"is_direct": True},
+        )
+        # Person that was invited joins the room
+        self.helper.join(room_id, invitee_user_id, tok=invitee_tok)
+
+        # Mimic the client setting the room as a direct message in the global account
+        # data
+        self.get_success(
+            self.store.add_account_data_for_user(
+                invitee_user_id,
+                AccountDataTypes.DIRECT,
+                {inviter_user_id: [room_id]},
+            )
+        )
+        self.get_success(
+            self.store.add_account_data_for_user(
+                inviter_user_id,
+                AccountDataTypes.DIRECT,
+                {invitee_user_id: [room_id]},
+            )
+        )
+
+        return room_id
+
+    def test_sync_list(self) -> None:
+        """
+        Test that room IDs show up in the Sliding Sync lists
+        """
+        alice_user_id = self.register_user("alice", "correcthorse")
+        alice_access_token = self.login(alice_user_id, "correcthorse")
+
+        room_id = self.helper.create_room_as(
+            alice_user_id, tok=alice_access_token, is_public=True
+        )
+
+        # Make the Sliding Sync request
+        channel = self.make_request(
+            "POST",
+            self.sync_endpoint,
+            {
+                "lists": {
+                    "foo-list": {
+                        "ranges": [[0, 99]],
+                        "required_state": [
+                            ["m.room.join_rules", ""],
+                            ["m.room.history_visibility", ""],
+                            ["m.space.child", "*"],
+                        ],
+                        "timeline_limit": 1,
+                    }
+                }
+            },
+            access_token=alice_access_token,
+        )
+        self.assertEqual(channel.code, 200, channel.json_body)
+
+        # Make sure it has the foo-list we requested
+        self.assertListEqual(
+            list(channel.json_body["lists"].keys()),
+            ["foo-list"],
+            channel.json_body["lists"].keys(),
+        )
+
+        # Make sure the list includes the room we are joined to
+        self.assertListEqual(
+            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            [
+                {
+                    "op": "SYNC",
+                    "range": [0, 99],
+                    "room_ids": [room_id],
+                }
+            ],
+            channel.json_body["lists"]["foo-list"],
+        )
+
+    def test_wait_for_sync_token(self) -> None:
+        """
+        Test that worker will wait until it catches up to the given token
+        """
+        alice_user_id = self.register_user("alice", "correcthorse")
+        alice_access_token = self.login(alice_user_id, "correcthorse")
+
+        # Create a future token that will cause us to wait. Since we never send a new
+        # event to reach that future stream_ordering, the worker will wait until the
+        # full timeout.
+        current_token = self.event_sources.get_current_token()
+        future_position_token = current_token.copy_and_replace(
+            StreamKeyType.ROOM,
+            RoomStreamToken(stream=current_token.room_key.stream + 1),
+        )
+
+        future_position_token_serialized = self.get_success(
+            future_position_token.to_string(self.store)
+        )
+
+        # Make the Sliding Sync request
+        channel = self.make_request(
+            "POST",
+            self.sync_endpoint + f"?pos={future_position_token_serialized}",
+            {
+                "lists": {
+                    "foo-list": {
+                        "ranges": [[0, 99]],
+                        "required_state": [
+                            ["m.room.join_rules", ""],
+                            ["m.room.history_visibility", ""],
+                            ["m.space.child", "*"],
+                        ],
+                        "timeline_limit": 1,
+                    }
+                }
+            },
+            access_token=alice_access_token,
+            await_result=False,
+        )
+        # Block for 10 seconds to make `notifier.wait_for_stream_token(from_token)`
+        # timeout
+        with self.assertRaises(TimedOutException):
+            channel.await_result(timeout_ms=9900)
+        channel.await_result(timeout_ms=200)
+        self.assertEqual(channel.code, 200, channel.json_body)
+
+        # We expect the `next_pos` in the result to be the same as what we requested
+        # with because we weren't able to find anything new yet.
+        self.assertEqual(
+            channel.json_body["next_pos"], future_position_token_serialized
+        )
+
+    def test_filter_list(self) -> None:
+        """
+        Test that filters apply to lists
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        # Create a DM room
+        dm_room_id = self._create_dm_room(
+            inviter_user_id=user1_id,
+            inviter_tok=user1_tok,
+            invitee_user_id=user2_id,
+            invitee_tok=user2_tok,
+        )
+
+        # Create a normal room
+        room_id = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+
+        # Make the Sliding Sync request
+        channel = self.make_request(
+            "POST",
+            self.sync_endpoint,
+            {
+                "lists": {
+                    "dms": {
+                        "ranges": [[0, 99]],
+                        "required_state": [],
+                        "timeline_limit": 1,
+                        "filters": {"is_dm": True},
+                    },
+                    "foo-list": {
+                        "ranges": [[0, 99]],
+                        "required_state": [],
+                        "timeline_limit": 1,
+                        "filters": {"is_dm": False},
+                    },
+                }
+            },
+            access_token=user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.json_body)
+
+        # Make sure it has the foo-list we requested
+        self.assertListEqual(
+            list(channel.json_body["lists"].keys()),
+            ["dms", "foo-list"],
+            channel.json_body["lists"].keys(),
+        )
+
+        # Make sure the list includes the room we are joined to
+        self.assertListEqual(
+            list(channel.json_body["lists"]["dms"]["ops"]),
+            [
+                {
+                    "op": "SYNC",
+                    "range": [0, 99],
+                    "room_ids": [dm_room_id],
+                }
+            ],
+            list(channel.json_body["lists"]["dms"]),
+        )
+        self.assertListEqual(
+            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            [
+                {
+                    "op": "SYNC",
+                    "range": [0, 99],
+                    "room_ids": [room_id],
+                }
+            ],
+            list(channel.json_body["lists"]["foo-list"]),
+        )
+
+    def test_sort_list(self) -> None:
+        """
+        Test that the lists are sorted by `stream_ordering`
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        room_id3 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+
+        # Activity that will order the rooms
+        self.helper.send(room_id3, "activity in room3", tok=user1_tok)
+        self.helper.send(room_id1, "activity in room1", tok=user1_tok)
+        self.helper.send(room_id2, "activity in room2", tok=user1_tok)
+
+        # Make the Sliding Sync request
+        channel = self.make_request(
+            "POST",
+            self.sync_endpoint,
+            {
+                "lists": {
+                    "foo-list": {
+                        "ranges": [[0, 99]],
+                        "required_state": [
+                            ["m.room.join_rules", ""],
+                            ["m.room.history_visibility", ""],
+                            ["m.space.child", "*"],
+                        ],
+                        "timeline_limit": 1,
+                    }
+                }
+            },
+            access_token=user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.json_body)
+
+        # Make sure it has the foo-list we requested
+        self.assertListEqual(
+            list(channel.json_body["lists"].keys()),
+            ["foo-list"],
+            channel.json_body["lists"].keys(),
+        )
+
+        # Make sure the list is sorted in the way we expect
+        self.assertListEqual(
+            list(channel.json_body["lists"]["foo-list"]["ops"]),
+            [
+                {
+                    "op": "SYNC",
+                    "range": [0, 99],
+                    "room_ids": [room_id2, room_id1, room_id3],
+                }
+            ],
+            channel.json_body["lists"]["foo-list"],
+        )
diff --git a/tests/rest/client/utils.py b/tests/rest/client/utils.py
index 7362bde7ab..f0ba40a1f1 100644
--- a/tests/rest/client/utils.py
+++ b/tests/rest/client/utils.py
@@ -330,9 +330,12 @@ class RestHelper:
             data,
         )
 
-        assert channel.code == expect_code, "Expected: %d, got: %d, resp: %r" % (
+        assert (
+            channel.code == expect_code
+        ), "Expected: %d, got: %d, PUT %s -> resp: %r" % (
             expect_code,
             channel.code,
+            path,
             channel.result["body"],
         )
 
diff --git a/tests/storage/test_event_chain.py b/tests/storage/test_event_chain.py
index 27d5b0125f..81feb3ec29 100644
--- a/tests/storage/test_event_chain.py
+++ b/tests/storage/test_event_chain.py
@@ -431,6 +431,7 @@ class EventChainStoreTestCase(HomeserverTestCase):
 
         for e in events:
             e.internal_metadata.stream_ordering = self._next_stream_ordering
+            e.internal_metadata.instance_name = self.hs.get_instance_name()
             self._next_stream_ordering += 1
 
         def _persist(txn: LoggingTransaction) -> None:
diff --git a/tests/storage/test_stream.py b/tests/storage/test_stream.py
index 2029cd9c68..fe1e873e15 100644
--- a/tests/storage/test_stream.py
+++ b/tests/storage/test_stream.py
@@ -19,7 +19,10 @@
 #
 #
 
-from typing import List
+import logging
+from typing import List, Tuple
+
+from immutabledict import immutabledict
 
 from twisted.test.proto_helpers import MemoryReactor
 
@@ -28,11 +31,13 @@ from synapse.api.filtering import Filter
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.types import JsonDict
+from synapse.types import JsonDict, PersistedEventPosition, RoomStreamToken
 from synapse.util import Clock
 
 from tests.unittest import HomeserverTestCase
 
+logger = logging.getLogger(__name__)
+
 
 class PaginationTestCase(HomeserverTestCase):
     """
@@ -268,3 +273,273 @@ class PaginationTestCase(HomeserverTestCase):
         }
         chunk = self._filter_messages(filter)
         self.assertEqual(chunk, [self.event_id_1, self.event_id_2, self.event_id_none])
+
+
+class GetLastEventInRoomBeforeStreamOrderingTestCase(HomeserverTestCase):
+    """
+    Test `get_last_event_pos_in_room_before_stream_ordering(...)`
+    """
+
+    servlets = [
+        admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.store = hs.get_datastores().main
+        self.event_sources = hs.get_event_sources()
+
+    def _update_persisted_instance_name_for_event(
+        self, event_id: str, instance_name: str
+    ) -> None:
+        """
+        Update the `instance_name` that persisted the the event in the database.
+        """
+        return self.get_success(
+            self.store.db_pool.simple_update_one(
+                "events",
+                keyvalues={"event_id": event_id},
+                updatevalues={"instance_name": instance_name},
+            )
+        )
+
+    def _send_event_on_instance(
+        self, instance_name: str, room_id: str, access_token: str
+    ) -> Tuple[JsonDict, PersistedEventPosition]:
+        """
+        Send an event in a room and mimic that it was persisted by a specific
+        instance/worker.
+        """
+        event_response = self.helper.send(
+            room_id, f"{instance_name} message", tok=access_token
+        )
+
+        self._update_persisted_instance_name_for_event(
+            event_response["event_id"], instance_name
+        )
+
+        event_pos = self.get_success(
+            self.store.get_position_for_event(event_response["event_id"])
+        )
+
+        return event_response, event_pos
+
+    def test_before_room_created(self) -> None:
+        """
+        Test that no event is returned if we are using a token before the room was even created
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        before_room_token = self.event_sources.get_current_token()
+
+        room_id = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+
+        last_event_result = self.get_success(
+            self.store.get_last_event_pos_in_room_before_stream_ordering(
+                room_id=room_id,
+                end_token=before_room_token.room_key,
+            )
+        )
+
+        self.assertIsNone(last_event_result)
+
+    def test_after_room_created(self) -> None:
+        """
+        Test that an event is returned if we are using a token after the room was created
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+
+        after_room_token = self.event_sources.get_current_token()
+
+        last_event_result = self.get_success(
+            self.store.get_last_event_pos_in_room_before_stream_ordering(
+                room_id=room_id,
+                end_token=after_room_token.room_key,
+            )
+        )
+        assert last_event_result is not None
+        last_event_id, _ = last_event_result
+
+        self.assertIsNotNone(last_event_id)
+
+    def test_activity_in_other_rooms(self) -> None:
+        """
+        Test to make sure that the last event in the room is returned even if the
+        `stream_ordering` has advanced from activity in other rooms.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        event_response = self.helper.send(room_id1, "target!", tok=user1_tok)
+        # Create another room to advance the stream_ordering
+        self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+
+        after_room_token = self.event_sources.get_current_token()
+
+        last_event_result = self.get_success(
+            self.store.get_last_event_pos_in_room_before_stream_ordering(
+                room_id=room_id1,
+                end_token=after_room_token.room_key,
+            )
+        )
+        assert last_event_result is not None
+        last_event_id, _ = last_event_result
+
+        # Make sure it's the event we expect (which also means we know it's from the
+        # correct room)
+        self.assertEqual(last_event_id, event_response["event_id"])
+
+    def test_activity_after_token_has_no_effect(self) -> None:
+        """
+        Test to make sure we return the last event before the token even if there is
+        activity after it.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        event_response = self.helper.send(room_id1, "target!", tok=user1_tok)
+
+        after_room_token = self.event_sources.get_current_token()
+
+        # Send some events after the token
+        self.helper.send(room_id1, "after1", tok=user1_tok)
+        self.helper.send(room_id1, "after2", tok=user1_tok)
+
+        last_event_result = self.get_success(
+            self.store.get_last_event_pos_in_room_before_stream_ordering(
+                room_id=room_id1,
+                end_token=after_room_token.room_key,
+            )
+        )
+        assert last_event_result is not None
+        last_event_id, _ = last_event_result
+
+        # Make sure it's the last event before the token
+        self.assertEqual(last_event_id, event_response["event_id"])
+
+    def test_last_event_within_sharded_token(self) -> None:
+        """
+        Test to make sure we can find the last event that that is *within* the sharded
+        token (a token that has an `instance_map` and looks like
+        `m{min_pos}~{writer1}.{pos1}~{writer2}.{pos2}`). We are specifically testing
+        that we can find an event within the tokens minimum and instance
+        `stream_ordering`.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        event_response1, event_pos1 = self._send_event_on_instance(
+            "worker1", room_id1, user1_tok
+        )
+        event_response2, event_pos2 = self._send_event_on_instance(
+            "worker1", room_id1, user1_tok
+        )
+        event_response3, event_pos3 = self._send_event_on_instance(
+            "worker1", room_id1, user1_tok
+        )
+
+        # Create another room to advance the `stream_ordering` on the same worker
+        # so we can sandwich event3 in the middle of the token
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        event_response4, event_pos4 = self._send_event_on_instance(
+            "worker1", room_id2, user1_tok
+        )
+
+        # Assemble a token that encompasses event1 -> event4 on worker1
+        end_token = RoomStreamToken(
+            stream=event_pos2.stream,
+            instance_map=immutabledict({"worker1": event_pos4.stream}),
+        )
+
+        # Send some events after the token
+        self.helper.send(room_id1, "after1", tok=user1_tok)
+        self.helper.send(room_id1, "after2", tok=user1_tok)
+
+        last_event_result = self.get_success(
+            self.store.get_last_event_pos_in_room_before_stream_ordering(
+                room_id=room_id1,
+                end_token=end_token,
+            )
+        )
+        assert last_event_result is not None
+        last_event_id, _ = last_event_result
+
+        # Should find closest event before the token in room1
+        self.assertEqual(
+            last_event_id,
+            event_response3["event_id"],
+            f"We expected {event_response3['event_id']} but saw {last_event_id} which corresponds to "
+            + str(
+                {
+                    "event1": event_response1["event_id"],
+                    "event2": event_response2["event_id"],
+                    "event3": event_response3["event_id"],
+                }
+            ),
+        )
+
+    def test_last_event_before_sharded_token(self) -> None:
+        """
+        Test to make sure we can find the last event that is *before* the sharded token
+        (a token that has an `instance_map` and looks like
+        `m{min_pos}~{writer1}.{pos1}~{writer2}.{pos2}`).
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        event_response1, event_pos1 = self._send_event_on_instance(
+            "worker1", room_id1, user1_tok
+        )
+        event_response2, event_pos2 = self._send_event_on_instance(
+            "worker1", room_id1, user1_tok
+        )
+
+        # Create another room to advance the `stream_ordering` on the same worker
+        room_id2 = self.helper.create_room_as(user1_id, tok=user1_tok, is_public=True)
+        event_response3, event_pos3 = self._send_event_on_instance(
+            "worker1", room_id2, user1_tok
+        )
+        event_response4, event_pos4 = self._send_event_on_instance(
+            "worker1", room_id2, user1_tok
+        )
+
+        # Assemble a token that encompasses event3 -> event4 on worker1
+        end_token = RoomStreamToken(
+            stream=event_pos3.stream,
+            instance_map=immutabledict({"worker1": event_pos4.stream}),
+        )
+
+        # Send some events after the token
+        self.helper.send(room_id1, "after1", tok=user1_tok)
+        self.helper.send(room_id1, "after2", tok=user1_tok)
+
+        last_event_result = self.get_success(
+            self.store.get_last_event_pos_in_room_before_stream_ordering(
+                room_id=room_id1,
+                end_token=end_token,
+            )
+        )
+        assert last_event_result is not None
+        last_event_id, _ = last_event_result
+
+        # Should find closest event before the token in room1
+        self.assertEqual(
+            last_event_id,
+            event_response2["event_id"],
+            f"We expected {event_response2['event_id']} but saw {last_event_id} which corresponds to "
+            + str(
+                {
+                    "event1": event_response1["event_id"],
+                    "event2": event_response2["event_id"],
+                }
+            ),
+        )
diff --git a/tests/storage/test_user_directory.py b/tests/storage/test_user_directory.py
index 156a610faa..c26932069f 100644
--- a/tests/storage/test_user_directory.py
+++ b/tests/storage/test_user_directory.py
@@ -711,6 +711,10 @@ class UserDirectoryICUTestCase(HomeserverTestCase):
             ),
         )
 
+        self.assertEqual(_parse_words_with_icu("user-1"), ["user-1"])
+        self.assertEqual(_parse_words_with_icu("user-ab"), ["user-ab"])
+        self.assertEqual(_parse_words_with_icu("user.--1"), ["user", "-1"])
+
     def test_regex_word_boundary_punctuation(self) -> None:
         """
         Tests the behaviour of punctuation with the non-ICU tokeniser
diff --git a/tests/test_visibility.py b/tests/test_visibility.py
index 3e2100eab4..89cbe4e54b 100644
--- a/tests/test_visibility.py
+++ b/tests/test_visibility.py
@@ -336,7 +336,6 @@ class FilterEventsForClientTestCase(HomeserverTestCase):
                 self.hs.get_storage_controllers(),
                 "@joiner:test",
                 events_to_filter,
-                msc4115_membership_on_events=True,
             )
         )
         resident_filtered_events = self.get_success(
@@ -344,7 +343,6 @@ class FilterEventsForClientTestCase(HomeserverTestCase):
                 self.hs.get_storage_controllers(),
                 "@resident:test",
                 events_to_filter,
-                msc4115_membership_on_events=True,
             )
         )
 
@@ -357,7 +355,7 @@ class FilterEventsForClientTestCase(HomeserverTestCase):
         self.assertEqual(
             ["join", "join", "leave"],
             [
-                e.unsigned[EventUnsignedContentFields.MSC4115_MEMBERSHIP]
+                e.unsigned[EventUnsignedContentFields.MEMBERSHIP]
                 for e in joiner_filtered_events
             ],
         )
@@ -379,7 +377,7 @@ class FilterEventsForClientTestCase(HomeserverTestCase):
         self.assertEqual(
             ["join", "join", "join", "join", "join"],
             [
-                e.unsigned[EventUnsignedContentFields.MSC4115_MEMBERSHIP]
+                e.unsigned[EventUnsignedContentFields.MEMBERSHIP]
                 for e in resident_filtered_events
             ],
         )
@@ -441,7 +439,6 @@ class FilterEventsOutOfBandEventsForClientTestCase(
                 self.hs.get_storage_controllers(),
                 "@user:test",
                 [invite_event, reject_event],
-                msc4115_membership_on_events=True,
             )
         )
         self.assertEqual(
@@ -451,7 +448,7 @@ class FilterEventsOutOfBandEventsForClientTestCase(
         self.assertEqual(
             ["invite", "leave"],
             [
-                e.unsigned[EventUnsignedContentFields.MSC4115_MEMBERSHIP]
+                e.unsigned[EventUnsignedContentFields.MEMBERSHIP]
                 for e in filtered_events
             ],
         )
@@ -463,7 +460,6 @@ class FilterEventsOutOfBandEventsForClientTestCase(
                     self.hs.get_storage_controllers(),
                     "@other:test",
                     [invite_event, reject_event],
-                    msc4115_membership_on_events=True,
                 )
             ),
             [],