# Matrix Specification Changes since last release


## Client-Server API

**Backwards Compatible Changes**

- [ ] Specify `unsigned.replaces_state` in client-formatted events. Contributed by @nexy7574. ([#2345](https://github.com/matrix-org/matrix-spec/issues/2345))
- [ ] Specify `m.key_backup` account data, as per [MSC4287](https://github.com/matrix-org/matrix-spec-proposals/pull/4287). ([#2354](https://github.com/matrix-org/matrix-spec/issues/2354))

**Spec Clarifications**

- [ ] Clarify SAS commitment calculation for `m.key.verification.accept` messages. ([#2344](https://github.com/matrix-org/matrix-spec/issues/2344))
- [ ] Clarify formats of string types. ([#2347](https://github.com/matrix-org/matrix-spec/issues/2347), [#2349](https://github.com/matrix-org/matrix-spec/issues/2349))
- [ ] Fix ordering of common error codes. ([#2348](https://github.com/matrix-org/matrix-spec/issues/2348))
- [ ] Clarify how to find `via` parameter when following room upgrades. ([#2352](https://github.com/matrix-org/matrix-spec/issues/2352))


## Server-Server API

**Breaking Changes**

- [ ] Require the `destination` field in server-to-server authentication. Contributed by @velikopter. ([#2360](https://github.com/matrix-org/matrix-spec/issues/2360))

**Spec Clarifications**

- [ ] Clarify how multiple signatures should be handled during signature verification. Contributed by @nexy7574. ([#2341](https://github.com/matrix-org/matrix-spec/issues/2341))


## Application Service API

No significant changes.


## Identity Service API

No significant changes.


## Push Gateway API

No significant changes.


## Room Versions

No significant changes.


## Appendices

No significant changes.


## Internal Changes/Tooling

**Spec Clarifications**

- [ ] Update and fix GitHub Actions. ([#2343](https://github.com/matrix-org/matrix-spec/issues/2343))
- [ ] Upgrade Docsy theme to v0.14.3. ([#2346](https://github.com/matrix-org/matrix-spec/issues/2346))