A group is a shared state, encrypted end to end, that lists its members, their roles and the group’s name and settings. Relays never see it. Each message to a group is encrypted once with the sender’s sender key and delivered to every member’s mailbox.
Sender keys
Each member has a sender key for each group, sent to every other member over their pairwise conversations. When anyone leaves or is removed, every remaining member generates a new sender key, so that a former member cannot read what is said after they go.
Changes to membership
Adding, removing and promoting members are signed changes to the group state. Each change refers to the one before it, so members can detect if anyone tries to show different members a different group.
Invitations
An invitation reveals the group’s name and the inviter, and nothing else, until it is accepted. In earlier versions an invitation also revealed how many members a group had, which could itself be sensitive. This was reported in the 2026 audit as GL4-L4 and fixed before release.
Groups may have up to 1,000 members. Larger audiences are better served by tools designed for broadcasting, which Glossia is not.