2 files changed, 6 insertions, 1 deletions
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index c2989765ce..f1c23d68e5 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -509,6 +509,10 @@ class SyncRestServlet(RestServlet):
             ephemeral_events = room.ephemeral
             result["ephemeral"] = {"events": ephemeral_events}
             result["unread_notifications"] = room.unread_notifications
+            if room.unread_thread_notifications:
+                result[
+                    "org.matrix.msc3773.unread_thread_notifications"
+                ] = room.unread_thread_notifications
             result["summary"] = room.summary
             if self._msc2654_enabled:
                 result["org.matrix.msc2654.unread_count"] = room.unread_count
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index c95b0d6f19..280d306483 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -103,8 +103,9 @@ class VersionsRestServlet(RestServlet):
                     "org.matrix.msc3030": self.config.experimental.msc3030_enabled,
                     # Adds support for thread relations, per MSC3440.
                     "org.matrix.msc3440.stable": True,  # TODO: remove when "v1.3" is added above
-                    # Support for thread read receipts.
+                    # Support for thread read receipts & notification counts.
                     "org.matrix.msc3771": self.config.experimental.msc3771_enabled,
+                    "org.matrix.msc3773": self.config.experimental.msc3773_enabled,
                     # Allows moderators to fetch redacted event content as described in MSC2815
                     "fi.mau.msc2815": self.config.experimental.msc2815_enabled,
                     # Adds support for login token requests as per MSC3882