Synapse 1.156.0rc1 (2026-06-30)

Features

Expose MSC4354 Sticky Events over MSC4186 (Simplified) Sliding Sync. (#19591)
Stabilize support for sending ephemeral events to application services, as per MSC2409. Contributed by @jason-famedly @ Famedly. (#19758)
Include allowed_room_ids in the /summary client-server API response for rooms with restricted join rules, as required by Matrix 1.15.
Contributed by @FrenchGithubUser @famedly. (#19762)
MSC4140: Cancellable delayed events: Allow authentication on delayed event management endpoints (such as /restart) to bypass ratelimits for unauthenticated requests based on the client IP address. (#19794)
Add new metric synapse_non_deactivated_user_count which tracks the number of non-deactivated users in the database, split by app_service. (#19848)
The GET /_matrix/client/unstable/org.matrix.msc1763/retention/configuration endpoint is now provided when retention
is enabled and experimental_features.msc1763_enabled is enabled, based on
MSC1763. (#19853)
Add experimental support for MSC4491: Invite reasons in room creation. (#19874)

Provide remote servers a way to find out about an event created during the remote join handshake. Contributed by @FrenchGithubUser and @jason-famedly @ Famedly. (#19390, #19855, #19856)
Advertise org.matrix.msc4143 in unstable_features when msc4143_enabled is set. (#19646)
Fix a long-standing bug where the badge notification count for a room could become permanently inflated if a read receipt was sent before the room's notification counts were first summarised. (#19785)
Fix startup listener logging to report the actual bound TCP port, so listeners configured with port 0 no longer log Synapse now listening on TCP port 0. (#19810)
Fix notification counts being inflated after a /purge_history when notifications had already been rotated into the summary table. (#19834)
Fix /sync caching transient errors for the sync_response_cache_duration. (#19845)
Fix local events being deleted by the Purge History admin API despite delete_local_events being set to false, in room versions other than 1 and 2. (#19850)
Fix a bug where a user's dehydrated device (MSC3814) was deleted when their device list was synced from Matrix Authentication Service (e.g. upon logging out their last device), breaking offline key delivery. (#19892)

Update auto_join_rooms config documentation to cover requirements for auto-joining invite-only rooms. (#19660)
Add stable endpoint for MSC3266: Room summary API into worker docs. Contributed by @olmari. (#19788)
Tweak wording of Rust crate dependency update policy. (#19829)
Fixed the Admin API user endpoint documentation examples to use JSON booleans (true/false) instead of numeric (0/1) values. (#19847)

Make simple_select_one_onecol_txn() more helpful by naming the table of the select - as all other query wrapper functions already did. (#19869)
Refactor get_user_which_could_invite logic to reuse get_users_which_can_issue_invite. Contributed by Noah Markert. (#19732)
Fix a flaky test (twisted.protocols.amp.TooLong error under trial -jN) caused by an oversized debug log line. (#19832)
Upload Complement test logs as CI artifacts instead of printing the raw output to the build log. (#19840)
Fix release script considering any workflow completion as successful. (#19843)
Force keyword-args for clear default_config(server_name="test") usage in test utilities. (#19849)
Add .ruff_cache/ directory to .gitignore. (#19854)
Bump poetry in CI from 2.2.1 to 2.4.1. (#19866, #19877)
Split out deferred and tokio_runtime to their own Rust modules. (#19868)
Prevent the cargo-test and cargo-bench CI jobs from being skipped, even on PRs that have Rust changes. (#19883)