Claude Code sessions can now message each other to coordinate parallel work

Message your other Claude Code sessions

Claude Code v2.1.224 adds cross-session messaging on macOS and Linux, enabled by default. Claude can proactively warn another session when a change breaks what that session is building, or pass along an answer one session found that another is blocked on. It uses ListAgents to discover reachable sessions and SendMessage to deliver plain-text messages—no conversation history or files are transferred. Common use cases: handing off a breaking-change alert, coordinating parallel worktrees, and getting status from long-running tasks. Cross-machine messaging requires Remote Control; admins can disable the feature entirely.

Why it matters: Claude Code cross-session messaging is a substantive Anthropic product update with a concrete mechanism and clear use cases. Hits all three HKR axes, but it's a toolchain iteration rather than a model capability breakthrough—lands at 78, featured tier.