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Room Versions

Rooms are central to how Matrix operates, and have strict rules for what is allowed to be contained within them. Rooms can also have various algorithms that handle different tasks, such as what to do when two or more events collide in the underlying DAG. To allow rooms to be improved upon through new algorithms or rules, “room versions” are employed to manage a set of expectations for each room. New room versions are assigned as needed.

There is no implicit ordering or hierarchy to room versions, and their principles are immutable once placed in the specification. Although there is a recommended set of versions, some rooms may benefit from features introduced by other versions. Rooms move between different versions by “upgrading” to the desired version. Due to versions not being ordered or hierarchical, this means a room can “upgrade” from version 2 to version 1, if it is so desired.

Feature matrix

Some functionality is only available in specific room versions, such as knocking. The table below shows which versions support which features from a client’s perspective. Server implementations are still welcome to reference the following table, however the detailed per-version specifications are more likely to be of interest.

Feature \ Version 1 2 3 4 5 6 7 8 9
Knocking ❌ ❌ ❌ ❌ ❌ ❌ ✔ ✔ ✔
Restricted join rules ❌ ❌ ❌ ❌ ❌ ❌ ❌ ✔ ✔

Complete list of room versions

Room versions are divided into two distinct groups: stable and unstable. Stable room versions may be used by rooms safely. Unstable room versions are everything else which is either not listed in the specification or flagged as unstable for some other reason. Versions can switch between stable and unstable periodically for a variety of reasons, including discovered security vulnerabilities and age.

Clients should not ask room administrators to upgrade their rooms if the room is running a stable version. Servers SHOULD use room version 6 as the default room version when creating new rooms.

The available room versions are:

  • Version 1 - Stable. The current version of most rooms.
  • Version 2 - Stable. Implements State Resolution Version 2.
  • Version 3 - Stable. Introduces events whose IDs are the event’s hash.
  • Version 4 - Stable. Builds on v3 by using URL-safe base64 for event IDs.
  • Version 5 - Stable. Introduces enforcement of signing key validity periods.
  • Version 6 - Stable. Alters several authorization rules for events.
  • Version 7 - Stable. Introduces knocking.
  • Version 8 - Stable. Adds a join rule to allow members of another room to join without invite.
  • Version 9 - Stable. Builds on v8 to fix issues when redacting some membership events.

Room version grammar

Room versions are used to change properties of rooms that may not be compatible with other servers. For example, changing the rules for event authorization would cause older servers to potentially end up in a split-brain situation due to not understanding the new rules.

A room version is defined as a string of characters which MUST NOT exceed 32 codepoints in length. Room versions MUST NOT be empty and SHOULD contain only the characters a-z, 0-9, ., and -.

Room versions are not intended to be parsed and should be treated as opaque identifiers. Room versions consisting only of the characters 0-9 and . are reserved for future versions of the Matrix protocol.

The complete grammar for a legal room version is:

room_version = 1*room_version_char
room_version_char = DIGIT
                  / %x61-7A         ; a-z
                  / "-" / "."

Examples of valid room versions are:

  • 1 (would be reserved by the Matrix protocol)
  • 1.2 (would be reserved by the Matrix protocol)
  • 1.2-beta
  • com.example.version