mpai is an open-source terminal tool that makes AI coding sessions multiplayer by letting a named teammate join an existing Codex or Claude Code conversation directly from their own terminal. The host runs one install command to share a specific session, and the guest joins via a private invite scoped only to that session over a Tailscale network. Each participant's prompts are attributed by name in the native transcript, with no screen sharing, transcript pasting, or new IDE required. mpai acts as a coordination layer above the agents, keeping session control with the host and sharing explicit and private by default.