Claude Code v2.1.224 introduces cross-session messaging: two or more parallel sessions of the same tool can exchange text messages. Claude uses two internal tools (ListAgents to discover reachable sessions and SendMessage to deliver the message) and decides on her own when to notify another session, for example after a change that breaks ongoing work elsewhere. The feature is active by default on macOS and Linux, with nothing to configure.

For anyone working with multiple terminals open, this changes how you coordinate work. Until now, every session was isolated: if one discovered a breaking change, it fell to you to copy and paste the information into the other. Now Claude can pass the information herself, and you can ask her to do it with a simple prompt like «Explain what we just did to the session working on the payments API».

The main use cases from the documentation: deliver a finding to someone working on another part of the repo, coordinate sessions operating on separate worktrees of the same project, have someone report the status of a long operation. Between different machines, the session can only respond, not initiate the exchange.

As we reported on August 5, release v2.1.222 had brought real worktree isolation between parallel agents. The logic follows: first you isolate, then you connect.

To try the feature, you need Claude Code v2.1.224 or higher on macOS or Linux. The official documentation is your starting point to see which sessions are reachable and how message delivery works.

In detail

What came before.

Until v2.1.222, every Claude Code session lived in its terminal without knowing what the others were doing. If you had three windows open on the same repository, the session modifying the payments module couldn’t notify the one writing tests for the same module. Information traveled through you: you read the output of one, copied it, pasted it in the other. Release v2.1.222 brought real worktree isolation, closing the risk that parallel sessions would step on each other’s files. Now v2.1.224 opens the channel in the opposite direction: isolated sessions can talk to each other.

How it works, without jargon.

Claude has two new tools at her disposal. ListAgents discovers which other active sessions she can reach on the machine. SendMessage delivers a text message to one of them by name. You never call these tools yourself: Claude uses them. You can ask her to send a message by writing a normal prompt, and she writes the content herself. You can also ask for nothing: if Claude understands that a change of hers has consequences for another session’s work, she can decide to notify it spontaneously.

The message is plain text. It doesn’t carry the conversation history or files. If you need to pass the full context of one session to another, the right function is still the session resume, not messaging.

The receiving session reads the message between one tool call and the next, during an active turn. A running tool is never interrupted. If the session is paused, Claude Code opens a new turn with the newly arrived message.

Same machine and cross-machine.

On the same machine, one session can write to another in both directions. Between different machines or toward the web, a session can only respond to a received message: it can’t initiate the exchange. The bridge between machines goes through Remote Control.

What changes for those orchestrating agents.

The multi-turn agent pattern enters a phase where sessions are no longer isolated but coordinated. Anyone already using Claude Code with multiple terminals open on the same project stops playing the human bridge between sessions. Anyone building orchestrations with Claude Code as the base runtime gains a native coordination channel, without needing to write external scripts to pass information between workers.

Limitations.

Messaging only runs on macOS and Linux, not Windows. Delivery isn’t guaranteed in every scenario: the documentation states it explicitly. Messages are text, not context. And the feature concerns the independent sessions you launch and guide: for teams of agents that Claude Code generates and supervises autonomously, another function already exists (agent teams) with its own coordination logic. Cross-session messaging doesn’t replace it, it stands alongside it for a different use case.