Claude Code sessions can now talk to each other

One session passes another a short summary rather than the full chat history and files, and the second session picks it up mid-task. It works both ways: you can ask a neighboring session a question and get the answer back in your active one. Per Anthropic's description, Claude also sends messages on its own, for instance when an edit it just made affects what another session is doing.

The messages travel through a mailbox mechanism inside agent teams, the experimental feature for running several sessions together. It's off by default. You turn it on with CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1 in settings.json or in your environment, and Anthropic's docs walk through the setup. macOS and Linux only, after updating Claude Code.