Support Matrix 1.18

Following https://github.com/element-hq/synapse/issues/19415

# Matrix Specification v1.18 Changelog

| | |
|---|---|
| Git commit | https://github.com/matrix-org/matrix-spec/tree/v1.18 |
| Release date | March 25, 2026 |

## Client-Server API

**New Endpoints**

- [ ] Add `GET /_matrix/client/v1/admin/suspend/{userId}`, as per [MSC4323](https://github.com/matrix-org/matrix-spec-proposals/pull/4323). ([#2278](https://github.com/matrix-org/matrix-spec/issues/2278))
- [ ] Add `PUT /_matrix/client/v1/admin/suspend/{userId}`, as per [MSC4323](https://github.com/matrix-org/matrix-spec-proposals/pull/4323). ([#2278](https://github.com/matrix-org/matrix-spec/issues/2278))
- [ ] Add `GET /_matrix/client/v1/admin/lock/{userId}`, as per [MSC4323](https://github.com/matrix-org/matrix-spec-proposals/pull/4323). ([#2278](https://github.com/matrix-org/matrix-spec/issues/2278))
- [ ] Add `PUT /_matrix/client/v1/admin/lock/{userId}`, as per [MSC4323](https://github.com/matrix-org/matrix-spec-proposals/pull/4323). ([#2278](https://github.com/matrix-org/matrix-spec/issues/2278))

**Removed Endpoints**

- [ ] The `score` request parameter on `/_matrix/client/v3/rooms/{roomId}/report/{eventId}` was removed as per [MSC4277](https://github.com/matrix-org/matrix-spec-proposals/pull/4277). ([#2311](https://github.com/matrix-org/matrix-spec/issues/2311))

**Backwards Compatible Changes**

- [ ] Add the account management capabilities for the OAuth 2.0 authentication API, as per [MSC4191](https://github.com/matrix-org/matrix-spec-proposals/pull/4191). ([#2270](https://github.com/matrix-org/matrix-spec/issues/2270))
- [ ] Add OAuth 2.0 aware clients, as per [MSC3824](https://github.com/matrix-org/matrix-spec-proposals/pull/3824). ([#2272](https://github.com/matrix-org/matrix-spec/issues/2272))
- [ ] Add administrator endpoints to lock and suspend server-local users and add the `m.account_management` capability, as per [MSC4323](https://github.com/matrix-org/matrix-spec-proposals/pull/4323). ([#2278](https://github.com/matrix-org/matrix-spec/issues/2278))
- [ ] Add `m.recent_emoji` account data event to track recently used emoji as per [MSC4356](https://github.com/matrix-org/matrix-spec-proposals/pull/4356). ([#2291](https://github.com/matrix-org/matrix-spec/issues/2291))
- [ ] Add `m.forget_forced_upon_leave` capability for servers to transparently auto-forget rooms that the user leaves as per [MSC4267](https://github.com/matrix-org/matrix-spec-proposals/pull/4267). ([#2292](https://github.com/matrix-org/matrix-spec/issues/2292))
- [ ] Add support for `m.room.redaction` events at the `PUT /rooms/{roomId}/send/{eventType}/{txnId}` endpoint, as per [MSC4169](https://github.com/matrix-org/matrix-spec-proposals/pull/4169). ([#2298](https://github.com/matrix-org/matrix-spec/issues/2298))
- [ ] Clients supporting the `ol` HTML element must also support the `start` attribute, as per [MSC4313](https://github.com/matrix-org/matrix-spec-proposals/pull/4313). ([#2299](https://github.com/matrix-org/matrix-spec/issues/2299))
- [ ] Add recommendation about excluding non-cross-signed devices from encrypted conversations, as per [MSC4153](https://github.com/matrix-org/matrix-spec-proposals/pull/4153). ([#2301](https://github.com/matrix-org/matrix-spec/issues/2301))
- [ ] Add invite blocking, as per [MSC4380](https://github.com/matrix-org/matrix-spec-proposals/pull/4380). ([#2305](https://github.com/matrix-org/matrix-spec/issues/2305))
- [ ] `/_matrix/client/v3/rooms/{roomId}/report` and `/_matrix/client/v3/rooms/{roomId}/report/{eventId}` may respond with HTTP 200 regardless of the reported subject's existence or add a random delay when generating responses as per [MSC4277](https://github.com/matrix-org/matrix-spec-proposals/pull/4277). ([#2311](https://github.com/matrix-org/matrix-spec/issues/2311))
- [ ] Add `M_USER_LIMIT_EXCEEDED` common error code, as per [MSC4335](https://github.com/matrix-org/matrix-spec-proposals/pull/4335). ([#2315](https://github.com/matrix-org/matrix-spec/issues/2315))
- [ ] Add the OAuth 2.0 Device Authorization Grant (RFC 8628) as a supported grant type, as per [MSC4341](https://github.com/matrix-org/matrix-spec-proposals/pull/4341). ([#2320](https://github.com/matrix-org/matrix-spec/issues/2320))
- [ ] Add the `is_animated` flag to the `info` object of the `m.image` msgtype and the `m.sticker` event, as per [MSC4230](https://github.com/matrix-org/matrix-spec-proposals/pull/4230). ([#2328](https://github.com/matrix-org/matrix-spec/issues/2328), [#2338](https://github.com/matrix-org/matrix-spec/issues/2338))
- [x] Add a "Policy Servers" module, as per [MSC4284](https://github.com/matrix-org/matrix-spec-proposals/pull/4284). ([#2332](https://github.com/matrix-org/matrix-spec/issues/2332))

**Spec Clarifications**

- [ ] The optional `submit_url` response parameter of the `/requestToken` endpoints uses the same request and response parameters and error codes as the Identity Service API's `POST /_matrix/identity/v2/validate/email/submitToken`, as per [MSC4183](https://github.com/matrix-org/matrix-spec-proposals/pull/4183). ([#2277](https://github.com/matrix-org/matrix-spec/issues/2277))
- [ ] Update non-historic mentions of matrix-doc repo to matrix-spec/-proposals. Contributed by @HarHarLinks. ([#2280](https://github.com/matrix-org/matrix-spec/issues/2280))
- [ ] Remove unintended TeX formatting. Contributed by @HarHarLinks. ([#2283](https://github.com/matrix-org/matrix-spec/issues/2283))
- [ ] Clarify the requiredness of `event_id` in `predecessor`. ([#2304](https://github.com/matrix-org/matrix-spec/issues/2304))
- [ ] Clarify terminology for keys in cross-signing module. ([#2306](https://github.com/matrix-org/matrix-spec/issues/2306))
- [ ] Add 404 responses to the OpenAPI of `GET /login` and `GET /auth_metadata` endpoints. The responses were already defined in text but not written in OpenAPI. ([#2316](https://github.com/matrix-org/matrix-spec/issues/2316))
- [x] Fix various typos throughout the specification. Contributed by @HarHarLinks. ([#2318](https://github.com/matrix-org/matrix-spec/issues/2318))
- [ ] Clarified attachment encryption to require secure generation of keys and hash verification. ([#2324](https://github.com/matrix-org/matrix-spec/issues/2324))
- [x] Order the common and other error codes alphabetically and remove duplicate `M_THREEPID_IN_USE` definition. ([#2336](https://github.com/matrix-org/matrix-spec/issues/2336))
- [x] Fix various typos throughout the specification. ([#2337](https://github.com/matrix-org/matrix-spec/issues/2337))

## Server-Server API

**Removed Endpoints**

- [ ] Remove `/v1/send_join` and `/v1/send_leave`, as per [MSC4376](https://github.com/matrix-org/matrix-spec-proposals/pull/4376). ([#2319](https://github.com/matrix-org/matrix-spec/issues/2319))

**Backwards Compatible Changes**

- [x] Add a concept of "Policy Servers", as per [MSC4284](https://github.com/matrix-org/matrix-spec-proposals/pull/4284). ([#2332](https://github.com/matrix-org/matrix-spec/issues/2332))

**Spec Clarifications**

- [ ] Clarify what the `minimum_valid_until_ts` field means when it is set in key queries. ([#2191](https://github.com/matrix-org/matrix-spec/issues/2191))
- [ ] Specify validation for PDUs passed to and returned from federation membership endpoints. ([#2284](https://github.com/matrix-org/matrix-spec/issues/2284))
- [ ] Specify that callers of `/_matrix/federation/v1/openid/userinfo` must validate the returned user ID. ([#2288](https://github.com/matrix-org/matrix-spec/issues/2288))
- [ ] Change `m.signing_update` typo to `m.signing_key_update`. Contributed by @velikopter ([#2300](https://github.com/matrix-org/matrix-spec/issues/2300))
- [ ] Add link to JSON signing algorithm in server-server auth section for clarity. Contributed by @thetayloredman. ([#2329](https://github.com/matrix-org/matrix-spec/issues/2329))
- [x] Fix various typos throughout the specification. ([#2338](https://github.com/matrix-org/matrix-spec/issues/2338))

## Application Service API

**Spec Clarifications**

- [x] Fix various typos throughout the specification. ([#2330](https://github.com/matrix-org/matrix-spec/issues/2330))

## Identity Service API

**Spec Clarifications**

- [ ] Clarify the error codes that can be returned with a 400 HTTP status code by the `POST /_matrix/identity/v2/validate/email/submitToken` and `POST /_matrix/identity/v2/validate/msisdn/submitToken` endpoints, introducing the `M_TOKEN_INCORRECT` error code, as per [MSC4183](https://github.com/matrix-org/matrix-spec-proposals/pull/4183). ([#2277](https://github.com/matrix-org/matrix-spec/issues/2277))
- [ ] Order the standard error codes alphabetically. ([#2336](https://github.com/matrix-org/matrix-spec/issues/2336))

## Push Gateway API

No significant changes.

## Room Versions

**Spec Clarifications**

- [ ] Clarify meaning of floating-point powerlevels. ([#2297](https://github.com/matrix-org/matrix-spec/issues/2297))
- [ ] Remove the post-1.16 release note for room version 12. ([#2303](https://github.com/matrix-org/matrix-spec/issues/2303))

## Appendices

**Spec Clarifications**

- [x] Add identifier pronunciation guidelines. Contributed by @HarHarLinks. ([#2307](https://github.com/matrix-org/matrix-spec/issues/2307))

## Internal Changes/Tooling

**Backwards Compatible Changes**

- [x] Include the spec release version in the filenames in the tarballs generated by CI. ([#2276](https://github.com/matrix-org/matrix-spec/issues/2276))

**Spec Clarifications**

- [x] Clarify vendor prefixing requirements. ([#2222](https://github.com/matrix-org/matrix-spec/issues/2222))
- [x] Auto-create draft releases when building release tags. ([#2275](https://github.com/matrix-org/matrix-spec/issues/2275))
- [x] Replace the Twitter link in the footer with our BlueSky and Mastodon socials. ([#2282](https://github.com/matrix-org/matrix-spec/issues/2282))
- [x] Upgrade to docsy v0.13.0. ([#2287](https://github.com/matrix-org/matrix-spec/issues/2287))
- [x] Updates to the release documentation. ([#2289](https://github.com/matrix-org/matrix-spec/issues/2289))
- [x] Remove unused leftover CSS files. ([#2290](https://github.com/matrix-org/matrix-spec/issues/2290))
- [x] Update the footer social links to match matrix.org. Contributed by @HarHarLinks. ([#2317](https://github.com/matrix-org/matrix-spec/issues/2317))
- [x] Fix various typos throughout the specification. Contributed by @HarHarLinks. ([#2318](https://github.com/matrix-org/matrix-spec/issues/2318))
- [x] Render error code sections as definition lists to improve readability. ([#2323](https://github.com/matrix-org/matrix-spec/issues/2323))

Review the linked predecessor issue #19415 and the unchecked entries in this Matrix Specification v1.18 changelog. No repository files, tests, or entry points are named, so first identify the affected Synapse API areas and the applicable MSC requirements; done means the remaining applicable checklist items are supported and verified.

Written by the indexing model from the issue text.