New in Claude Code: your sessions can now message each other. Instead of having

Claude Code's cross-session messaging lets one running session pass a short written note to another, so a user does not have to re-explain the same context in a second terminal. Anthropic's August 7 announcement says Claude sends a summary, not the conversation history or files, and the other session picks it up mid-task.

The Claude Code documentation explains the mechanics. Claude finds the target session with a `ListAgents` tool and sends the note with `SendMessage`. The user can ask for a message, or Claude can send one on its own, for example after making a change that affects work another session is doing. A busy session reads the message between tool calls, so a running tool is not interrupted, and an idle session starts a new turn with it. To move a whole conversation instead, the documentation points to resuming the session.

The receiving session treats the note as coming from another session, not from the user. The note cannot answer a pending permission prompt, commands in its text are not executed, Claude is instructed not to change permission settings or `CLAUDE.md` because another session asked, and the receiving session's own permission prompts still apply. A session can also hold or refuse incoming messages. These details come from the current documentation, which lists later additions such as @-mentioning a session by name (v2.1.232) and native Windows support (v2.1.234); the feature itself requires v2.1.224 or later on macOS and Linux.