Antimatter
Legal

Privacy policy

Last updated: 16 October 2026.

This page covers two things: the Antimatter software, which organisations run on their own servers, and this website, antimatter.chat.

The Antimatter software

Antimatter is self-hosted. When you use an Antimatter server, the organisation that runs it decides what data is kept, for how long and who can access it. The Antimatter project has no access to your server, your account or your messages. For questions about your data on a particular server, contact its administrators; their own privacy policy applies.

What the software does by itself:

  • No telemetry. The server doesn't send usage statistics, diagnostics or any other data to the Antimatter project, to Mattermost, Inc. (whose software Antimatter is based on) or to other third parties.
  • Outside connections only for features an administrator turns on, to the services they configure: for example a push notification service, a GIF provider, an email server, an identity provider for single sign-on, or AI, speech or translation models.
  • Two exceptions, on by default, which administrators can turn off. Link previews: when someone posts a link, the server fetches that page to show its title and picture. And calls: they use Cloudflare's public STUN server (stun.cloudflare.com) to find public network addresses. The server asks it when the Calls app starts, and each person's device asks it when they join a call. Cloudflare sees only the IP address and port of the server and of each person joining, not the call itself. Administrators can use their own STUN server instead, or none; see Calls and voice.
  • AI features use the models the administrator chooses. When they're hosted by a third party, what is sent to them (a message to rewrite, a conversation to summarize, the audio of a transcribed call) goes to that provider. Administrators can use self-hosted models so that nothing leaves their network.

This website

  • antimatter.chat is a static website hosted on GitHub Pages.
  • It sets no cookies, and uses no analytics, trackers or advertising. Its fonts and images are served from the site itself, so your browser makes no requests to other websites while you read it.
  • Like any web host, GitHub receives your IP address and the pages you request, to serve them. See the GitHub Privacy Statement.
  • If you open an issue or contribute on GitHub, what you post there is public and handled by GitHub under its own terms.

Contact

For questions about this policy, open an issue in the Antimatter community repository.

We may update this policy; the date at the top says when it last changed.