- Add experimental support for [MSC4388: Secure out-of-band channel for sign in with QR](https://github.com/matrix-org/matrix-spec-proposals/pull/4388). ([\#19127](https://github.com/element-hq/synapse/issues/19127)) - Add stable support for [MSC4380](https://github.com/matrix-org/matrix-spec-proposals/pull/4380) invite blocking. ([\#19431](https://github.com/element-hq/synapse/issues/19431)) - Fix the 'Login as a user' Admin API not checking if the user exists before issuing an access token. ([\#18518](https://github.com/element-hq/synapse/issues/18518)) - Fix `/sync` missing membership event in `state_after` (experimental [MSC4222](https://github.com/matrix-org/matrix-spec-proposals/pull/4222) implementation) in some scenarios. ([\#19460](https://github.com/element-hq/synapse/issues/19460)) - Add log to explain when and why we freeze objects in the garbage collector. ([\#19440](https://github.com/element-hq/synapse/issues/19440)) - Better instrument `JoinRoomAliasServlet` with tracing. ([\#19461](https://github.com/element-hq/synapse/issues/19461)) - Fix Complement CI not running against the code from our PRs. ([\#19475](https://github.com/element-hq/synapse/issues/19475)) - Log `docker system info` in CI so we have a plain record of how GitHub runners evolve over time. ([\#19480](https://github.com/element-hq/synapse/issues/19480)) - Rename the `test_disconnect` test helper so that pytest doesn't see it as a test. ([\#19486](https://github.com/element-hq/synapse/issues/19486)) - Add a log line when we delete devices. Contributed by @bradtgmurray @ Beeper. ([\#19496](https://github.com/element-hq/synapse/issues/19496)) - Pre-allocate the buffer based on the expected `Content-Length` with the Rust HTTP client. ([\#19498](https://github.com/element-hq/synapse/issues/19498)) - Cancel long-running sync requests if the client has gone away. ([\#19499](https://github.com/element-hq/synapse/issues/19499)) - Try and reduce reactor tick times when under heavy load. ([\#19507](https://github.com/element-hq/synapse/issues/19507)) - Simplify Rust HTTP client response streaming and limiting. ([\#19510](https://github.com/element-hq/synapse/issues/19510)) - Replace deprecated collection import locations with current locations. ([\#19515](https://github.com/element-hq/synapse/issues/19515)) - Bump most locked Python dependencies to their latest versions. ([\#19519](https://github.com/element-hq/synapse/issues/19519))