diff --git a/CHANGES.md b/CHANGES.md
index 91fe74c60f..8ed2bb2400 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,70 @@
+# Synapse 1.139.0rc1 (2025-09-23)
+
+## Features
+
+- Add experimental support for [MSC4308: Thread Subscriptions extension to Sliding Sync](https://github.com/matrix-org/matrix-spec-proposals/pull/4308) when [MSC4306: Thread Subscriptions](https://github.com/matrix-org/matrix-spec-proposals/pull/4306) and [MSC4186: Simplified Sliding Sync](https://github.com/matrix-org/matrix-spec-proposals/pull/4186) are enabled. ([\#18695](https://github.com/element-hq/synapse/issues/18695))
+- Update push rules for experimental [MSC4306: Thread Subscriptions](https://github.com/matrix-org/matrix-doc/issues/4306) to follow a newer draft. ([\#18846](https://github.com/element-hq/synapse/issues/18846))
+- Add `get_media_upload_limits_for_user` and `on_media_upload_limit_exceeded` module API callbacks to the media repository. ([\#18848](https://github.com/element-hq/synapse/issues/18848))
+- Support [MSC4169](https://github.com/matrix-org/matrix-spec-proposals/pull/4169) for backwards-compatible redaction sending using the `/send` endpoint. Contributed by @SpiritCroc @ Beeper. ([\#18898](https://github.com/element-hq/synapse/issues/18898))
+- Add an in-memory cache to `_get_e2e_cross_signing_signatures_for_devices` to reduce DB load. ([\#18899](https://github.com/element-hq/synapse/issues/18899))
+
+## Bugfixes
+
+- Ensure all PDUs sent via `/send` pass canonical JSON checks. ([\#18641](https://github.com/element-hq/synapse/issues/18641))
+- Fix bug where we did not send invite revocations over federation. ([\#18823](https://github.com/element-hq/synapse/issues/18823))
+- Fix prefixed support for [MSC4133](https://github.com/matrix-org/matrix-spec-proposals/pull/4133). ([\#18875](https://github.com/element-hq/synapse/issues/18875))
+- Fix open redirect in legacy SSO flow with the `idp` query parameter. ([\#18909](https://github.com/element-hq/synapse/issues/18909))
+- Fix a performance regression related to the experimental Delayed Events ([MSC4140](https://github.com/matrix-org/matrix-spec-proposals/pull/4140)) feature. ([\#18926](https://github.com/element-hq/synapse/issues/18926))
+
+## Updates to the Docker image
+
+- Suppress "Applying schema" log noise bulk when `SYNAPSE_LOG_TESTING` is set. ([\#18878](https://github.com/element-hq/synapse/issues/18878))
+
+## Improved Documentation
+
+- Clarify Python dependency constraints in our deprecation policy. ([\#18856](https://github.com/element-hq/synapse/issues/18856))
+- Clarify necessary `jwt_config` parameter in OIDC documentation for authentik. Contributed by @maxkratz. ([\#18931](https://github.com/element-hq/synapse/issues/18931))
+
+## Deprecations and Removals
+
+- Remove obsolete and experimental `/sync/e2ee` endpoint. ([\#18583](https://github.com/element-hq/synapse/issues/18583))
+
+## Internal Changes
+
+- Fix `LaterGauge` metrics to collect from all servers. ([\#18791](https://github.com/element-hq/synapse/issues/18791))
+- Configure Synapse to run [MSC4306: Thread Subscriptions](https://github.com/matrix-org/matrix-spec-proposals/pull/4306) Complement tests. ([\#18819](https://github.com/element-hq/synapse/issues/18819))
+- Remove `sentinel` logcontext usage where we log in `setup`, `start` and `exit`. ([\#18870](https://github.com/element-hq/synapse/issues/18870))
+- Use the `Enum`'s value for the dictionary key when responding to an admin request for experimental features. ([\#18874](https://github.com/element-hq/synapse/issues/18874))
+- Start background tasks after we fork the process (daemonize). ([\#18886](https://github.com/element-hq/synapse/issues/18886))
+- Better explain how we manage the logcontext in `run_in_background(...)` and `run_as_background_process(...)`. ([\#18900](https://github.com/element-hq/synapse/issues/18900), [\#18906](https://github.com/element-hq/synapse/issues/18906))
+- Remove `sentinel` logcontext usage in `Clock` utilities like `looping_call` and `call_later`. ([\#18907](https://github.com/element-hq/synapse/issues/18907))
+- Replace usages of the deprecated `pkg_resources` interface in preparation of setuptools dropping it soon. ([\#18910](https://github.com/element-hq/synapse/issues/18910))
+- Split loading config from homeserver `setup`. ([\#18933](https://github.com/element-hq/synapse/issues/18933))
+- Fix `run_in_background` not being awaited properly in some tests causing `LoggingContext` problems. ([\#18937](https://github.com/element-hq/synapse/issues/18937))
+- Fix `run_as_background_process` not being awaited properly causing `LoggingContext` problems in experimental [MSC4140](https://github.com/matrix-org/matrix-spec-proposals/pull/4140): Delayed events implementation. ([\#18938](https://github.com/element-hq/synapse/issues/18938))
+- Introduce `Clock.call_when_running(...)` to wrap startup code in a logcontext, ensuring we can identify which server generated the logs. ([\#18944](https://github.com/element-hq/synapse/issues/18944))
+- Introduce `Clock.add_system_event_trigger(...)` to wrap system event callback code in a logcontext, ensuring we can identify which server generated the logs. ([\#18945](https://github.com/element-hq/synapse/issues/18945))
+- Update [MSC4190](https://github.com/matrix-org/matrix-spec-proposals/pull/4190) support to return correct errors and allow appservices to reset cross-signing keys without user-interactive authentication. Contributed by @tulir @ Beeper. ([\#18946](https://github.com/element-hq/synapse/issues/18946))
+
+
+
+### Updates to locked dependencies
+
+* Bump actions/setup-go from 5.5.0 to 6.0.0. ([\#18891](https://github.com/element-hq/synapse/issues/18891))
+* Bump actions/setup-python from 5.6.0 to 6.0.0. ([\#18890](https://github.com/element-hq/synapse/issues/18890))
+* Bump authlib from 1.6.1 to 1.6.3. ([\#18921](https://github.com/element-hq/synapse/issues/18921))
+* Bump jsonschema from 4.25.0 to 4.25.1. ([\#18897](https://github.com/element-hq/synapse/issues/18897))
+* Bump log from 0.4.27 to 0.4.28. ([\#18892](https://github.com/element-hq/synapse/issues/18892))
+* Bump phonenumbers from 9.0.12 to 9.0.13. ([\#18893](https://github.com/element-hq/synapse/issues/18893))
+* Bump pydantic from 2.11.7 to 2.11.9. ([\#18922](https://github.com/element-hq/synapse/issues/18922))
+* Bump serde from 1.0.219 to 1.0.223. ([\#18920](https://github.com/element-hq/synapse/issues/18920))
+* Bump serde_json from 1.0.143 to 1.0.145. ([\#18919](https://github.com/element-hq/synapse/issues/18919))
+* Bump sigstore/cosign-installer from 3.9.2 to 3.10.0. ([\#18917](https://github.com/element-hq/synapse/issues/18917))
+* Bump towncrier from 24.8.0 to 25.8.0. ([\#18894](https://github.com/element-hq/synapse/issues/18894))
+* Bump types-psycopg2 from 2.9.21.20250809 to 2.9.21.20250915. ([\#18918](https://github.com/element-hq/synapse/issues/18918))
+* Bump types-requests from 2.32.4.20250611 to 2.32.4.20250809. ([\#18895](https://github.com/element-hq/synapse/issues/18895))
+* Bump types-setuptools from 80.9.0.20250809 to 80.9.0.20250822. ([\#18924](https://github.com/element-hq/synapse/issues/18924))
+
 # Synapse 1.138.0 (2025-09-09)
 
 No significant changes since 1.138.0rc1.
diff --git a/changelog.d/18583.removal b/changelog.d/18583.removal
deleted file mode 100644
index d7baa85147..0000000000
--- a/changelog.d/18583.removal
+++ /dev/null
@@ -1 +0,0 @@
-Remove obsolete and experimental `/sync/e2ee` endpoint.
\ No newline at end of file
diff --git a/changelog.d/18641.bugfix b/changelog.d/18641.bugfix
deleted file mode 100644
index 8f2a2e3d8b..0000000000
--- a/changelog.d/18641.bugfix
+++ /dev/null
@@ -1 +0,0 @@
-Ensure all PDUs sent via `/send` pass canonical JSON checks.
diff --git a/changelog.d/18695.feature b/changelog.d/18695.feature
deleted file mode 100644
index 1481a27f23..0000000000
--- a/changelog.d/18695.feature
+++ /dev/null
@@ -1 +0,0 @@
-Add experimental support for [MSC4308: Thread Subscriptions extension to Sliding Sync](https://github.com/matrix-org/matrix-spec-proposals/pull/4308) when [MSC4306: Thread Subscriptions](https://github.com/matrix-org/matrix-spec-proposals/pull/4306) and [MSC4186: Simplified Sliding Sync](https://github.com/matrix-org/matrix-spec-proposals/pull/4186) are enabled.
\ No newline at end of file
diff --git a/changelog.d/18791.misc b/changelog.d/18791.misc
deleted file mode 100644
index 6ecd498286..0000000000
--- a/changelog.d/18791.misc
+++ /dev/null
@@ -1 +0,0 @@
-Fix `LaterGauge` metrics to collect from all servers.
diff --git a/changelog.d/18819.misc b/changelog.d/18819.misc
deleted file mode 100644
index c76e050e79..0000000000
--- a/changelog.d/18819.misc
+++ /dev/null
@@ -1 +0,0 @@
-Configure Synapse to run MSC4306: Thread Subscriptions Complement tests.
\ No newline at end of file
diff --git a/changelog.d/18823.bugfix b/changelog.d/18823.bugfix
deleted file mode 100644
index 473c865aa4..0000000000
--- a/changelog.d/18823.bugfix
+++ /dev/null
@@ -1 +0,0 @@
-Fix bug where we did not send invite revocations over federation.
diff --git a/changelog.d/18846.feature b/changelog.d/18846.feature
deleted file mode 100644
index 4a873d4446..0000000000
--- a/changelog.d/18846.feature
+++ /dev/null
@@ -1 +0,0 @@
-Update push rules for experimental [MSC4306: Thread Subscriptions](https://github.com/matrix-org/matrix-doc/issues/4306) to follow newer draft.
\ No newline at end of file
diff --git a/changelog.d/18848.feature b/changelog.d/18848.feature
deleted file mode 100644
index 302a6e7b66..0000000000
--- a/changelog.d/18848.feature
+++ /dev/null
@@ -1 +0,0 @@
-Add `get_media_upload_limits_for_user` and `on_media_upload_limit_exceeded` module API callbacks for media repository.
diff --git a/changelog.d/18856.doc b/changelog.d/18856.doc
deleted file mode 100644
index 0e5e55377f..0000000000
--- a/changelog.d/18856.doc
+++ /dev/null
@@ -1 +0,0 @@
-Clarify Python dependency constraints in our deprecation policy.
diff --git a/changelog.d/18870.misc b/changelog.d/18870.misc
deleted file mode 100644
index e54ba4f37a..0000000000
--- a/changelog.d/18870.misc
+++ /dev/null
@@ -1 +0,0 @@
-Remove `sentinel` logcontext usage where we log in `setup`, `start` and exit.
diff --git a/changelog.d/18874.misc b/changelog.d/18874.misc
deleted file mode 100644
index 729befb5e8..0000000000
--- a/changelog.d/18874.misc
+++ /dev/null
@@ -1 +0,0 @@
-Use the `Enum`'s value for the dictionary key when responding to an admin request for experimental features.
diff --git a/changelog.d/18875.bugfix b/changelog.d/18875.bugfix
deleted file mode 100644
index 3bda7a1d18..0000000000
--- a/changelog.d/18875.bugfix
+++ /dev/null
@@ -1 +0,0 @@
-Fix prefixed support for MSC4133.
diff --git a/changelog.d/18878.docker b/changelog.d/18878.docker
deleted file mode 100644
index cf74f67cc8..0000000000
--- a/changelog.d/18878.docker
+++ /dev/null
@@ -1 +0,0 @@
-Suppress "Applying schema" log noise bulk when `SYNAPSE_LOG_TESTING` is set.
diff --git a/changelog.d/18886.misc b/changelog.d/18886.misc
deleted file mode 100644
index d0d32e59ab..0000000000
--- a/changelog.d/18886.misc
+++ /dev/null
@@ -1 +0,0 @@
-Start background tasks after we fork the process (daemonize).
diff --git a/changelog.d/18898.feature b/changelog.d/18898.feature
deleted file mode 100644
index bf31dd55d1..0000000000
--- a/changelog.d/18898.feature
+++ /dev/null
@@ -1 +0,0 @@
-Support [MSC4169](https://github.com/matrix-org/matrix-spec-proposals/pull/4169) for backwards-compatible redaction sending using the `/send` endpoint. Contributed by @SpiritCroc @ Beeper.
diff --git a/changelog.d/18899.feature b/changelog.d/18899.feature
deleted file mode 100644
index ee7141efc5..0000000000
--- a/changelog.d/18899.feature
+++ /dev/null
@@ -1 +0,0 @@
-Add an in-memory cache to `_get_e2e_cross_signing_signatures_for_devices` to reduce DB load.
\ No newline at end of file
diff --git a/changelog.d/18900.misc b/changelog.d/18900.misc
deleted file mode 100644
index d7d8b47eb0..0000000000
--- a/changelog.d/18900.misc
+++ /dev/null
@@ -1 +0,0 @@
-Better explain how we manage the logcontext in `run_in_background(...)` and `run_as_background_process(...)`.
diff --git a/changelog.d/18906.misc b/changelog.d/18906.misc
deleted file mode 100644
index d7d8b47eb0..0000000000
--- a/changelog.d/18906.misc
+++ /dev/null
@@ -1 +0,0 @@
-Better explain how we manage the logcontext in `run_in_background(...)` and `run_as_background_process(...)`.
diff --git a/changelog.d/18907.misc b/changelog.d/18907.misc
deleted file mode 100644
index 4fca9ec8fb..0000000000
--- a/changelog.d/18907.misc
+++ /dev/null
@@ -1 +0,0 @@
-Remove `sentinel` logcontext usage in `Clock` utilities like `looping_call` and `call_later`.
diff --git a/changelog.d/18909.bugfix b/changelog.d/18909.bugfix
deleted file mode 100644
index 10d17631f0..0000000000
--- a/changelog.d/18909.bugfix
+++ /dev/null
@@ -1 +0,0 @@
-Fix open redirect in legacy SSO flow with the `idp` query parameter.
diff --git a/changelog.d/18910.misc b/changelog.d/18910.misc
deleted file mode 100644
index d5bd3ef314..0000000000
--- a/changelog.d/18910.misc
+++ /dev/null
@@ -1 +0,0 @@
-Replace usages of the deprecated `pkg_resources` interface in preparation of setuptools dropping it soon.
\ No newline at end of file
diff --git a/changelog.d/18926.bugfix b/changelog.d/18926.bugfix
deleted file mode 100644
index c450313764..0000000000
--- a/changelog.d/18926.bugfix
+++ /dev/null
@@ -1 +0,0 @@
-Fix a performance regression related to the experimental Delayed Events ([MSC4140](https://github.com/matrix-org/matrix-spec-proposals/pull/4140)) feature.
\ No newline at end of file
diff --git a/changelog.d/18931.doc b/changelog.d/18931.doc
deleted file mode 100644
index 8a2dcb8654..0000000000
--- a/changelog.d/18931.doc
+++ /dev/null
@@ -1,2 +0,0 @@
-Clarify necessary `jwt_config` parameter in OIDC documentation for authentik.
-Contributed by @maxkratz.
diff --git a/changelog.d/18933.misc b/changelog.d/18933.misc
deleted file mode 100644
index 3308d367e7..0000000000
--- a/changelog.d/18933.misc
+++ /dev/null
@@ -1 +0,0 @@
-Split loading config from homeserver `setup`.
diff --git a/changelog.d/18937.misc b/changelog.d/18937.misc
deleted file mode 100644
index ab1e9c4d47..0000000000
--- a/changelog.d/18937.misc
+++ /dev/null
@@ -1 +0,0 @@
-Fix `run_in_background` not be awaited properly in some tests causing `LoggingContext` problems.
diff --git a/changelog.d/18938.misc b/changelog.d/18938.misc
deleted file mode 100644
index ab31cb7299..0000000000
--- a/changelog.d/18938.misc
+++ /dev/null
@@ -1 +0,0 @@
-Fix `run_as_background_process` not be awaited properly causing `LoggingContext` problems in experimental [MSC4140](https://github.com/matrix-org/matrix-spec-proposals/pull/4140): Delayed events implementation.
diff --git a/changelog.d/18944.misc b/changelog.d/18944.misc
deleted file mode 100644
index 9561aa9275..0000000000
--- a/changelog.d/18944.misc
+++ /dev/null
@@ -1 +0,0 @@
-Introduce `Clock.call_when_running(...)` to wrap startup code in a logcontext, ensuring we can identify which server generated the logs.
diff --git a/changelog.d/18945.misc b/changelog.d/18945.misc
deleted file mode 100644
index e49077c8f2..0000000000
--- a/changelog.d/18945.misc
+++ /dev/null
@@ -1 +0,0 @@
-Introduce `Clock.add_system_event_trigger(...)` to wrap system event callback code in a logcontext, ensuring we can identify which server generated the logs.
diff --git a/changelog.d/18946.misc b/changelog.d/18946.misc
deleted file mode 100644
index 53c246a638..0000000000
--- a/changelog.d/18946.misc
+++ /dev/null
@@ -1 +0,0 @@
-Update [MSC4190](https://github.com/matrix-org/matrix-spec-proposals/pull/4190) support to return correct errors and allow appservices to reset cross-signing keys without user-interactive authentication. Contributed by @tulir @ Beeper.
diff --git a/debian/changelog b/debian/changelog
index 035d06ad2b..f047143923 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,9 @@
+matrix-synapse-py3 (1.139.0~rc1) stable; urgency=medium
+
+  * New Synapse release 1.139.0rc1.
+
+ -- Synapse Packaging team <packages@matrix.org>  Tue, 23 Sep 2025 13:24:50 +0100
+
 matrix-synapse-py3 (1.138.0) stable; urgency=medium
 
   * New Synapse release 1.138.0.
diff --git a/pyproject.toml b/pyproject.toml
index f9dd0ca26b..68824812ba 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -101,7 +101,7 @@ module-name = "synapse.synapse_rust"
 
 [tool.poetry]
 name = "matrix-synapse"
-version = "1.138.0"
+version = "1.139.0rc1"
 description = "Homeserver for the Matrix decentralised comms protocol"
 authors = ["Matrix.org Team and Contributors <packages@matrix.org>"]
 license = "AGPL-3.0-or-later"
diff --git a/schema/synapse-config.schema.yaml b/schema/synapse-config.schema.yaml
index fdce4219ae..2a7f94a700 100644
--- a/schema/synapse-config.schema.yaml
+++ b/schema/synapse-config.schema.yaml
@@ -1,5 +1,5 @@
 $schema: https://element-hq.github.io/synapse/latest/schema/v1/meta.schema.json
-$id: https://element-hq.github.io/synapse/schema/synapse/v1.138/synapse-config.schema.json
+$id: https://element-hq.github.io/synapse/schema/synapse/v1.139/synapse-config.schema.json
 type: object
 properties:
   modules: