Messages move between your sessions
Claude Code can now let one of your sessions send a message straight to another one, according to Anthropic’s documentation. Cross-session messaging requires version 2.1.224 on macOS and Linux, including WSL 2. Native Windows requires version 2.1.234. Where it’s available, it’s on automatically. There’s nothing to turn on.
This helps if you run more than one Claude Code session at a time. That might mean working in separate worktrees, isolated copies of the same repository that let you work on multiple branches side by side, or watching a long migration run in another terminal. Either way, it replaces some of the copy-pasting between windows. Claude can now tell another one of your sessions that database structure changed, that a data migration finished, or that branches are ready to combine.
Two tools make this work: ListAgents, which finds which of your sessions Claude can reach, and SendMessage, which delivers text to one of them by name. A message is only text. It never carries the sending session’s full conversation history or files, and it can’t run commands. If a message contains something that looks like an instruction, such as /compact, Claude Code treats it as plain text rather than executing it.
Every incoming message lands in one of three states: delivered straight to the receiving Claude, held until you approve it, or refused and dropped without ever reaching Claude.
Why it matters
Delivery depends on each session’s permissions. This connects to Anthropic’s default-mode announcement, which scheduled auto mode as the default on Pro, Max, and Team for August 14. Auto mode replaces the usual “approve this command?” prompts with a built-in checker that clears routine actions on its own and can seek approval or a safer path when it blocks an action.
When you haven’t set a rule yourself, Claude Code sorts each session into one of two groups. Sessions that skip permission prompts entirely, meaning nothing about their work gets checked with you at all, count as “bypassing.” Other modes, including auto mode, count as “prompting” for message delivery.
A message between two “prompting” sessions is delivered immediately, without an approval dialog. Messages between the two groups are held for approval. Messages between two bypassing sessions are delivered.
Auto mode falls into the “prompting” group. Anthropic scheduled it as the default on Pro, Max, and Team for August 14. Sessions using auto mode can therefore pass messages to each other automatically, with no popup to click through. It’s the same tradeoff auto mode already makes for individual commands, now extended to messages between your own sessions.
This is narrower than it might sound. A message from another session can never approve a permission prompt on your behalf, and Claude Code explicitly instructs the receiving session never to change settings or your CLAUDE.md project instructions because another session asked. Whatever the message asks the receiving session to do still has to clear that session’s own permission rules, the same way any other request would. Messaging does not grant the receiving session new permissions.
What it can do is put misleading text in front of a session that would otherwise trust its own judgment. Say one of your sessions reads a webpage or file with hidden instructions planted by an attacker, a trick known as prompt injection, and gets fooled into believing them. It could now pass that bad framing along to a second session automatically, with no approval screen in between. The second session still needs its own permissions to act on it, but a well-worded message could talk it into using access it already has in a way you didn’t intend.
Who should care
This affects anyone running multiple sessions, including parallel worktrees, long migrations, or background agents.
Same-machine messaging on Amazon Bedrock, Claude Platform on AWS, Google Cloud’s Agent Platform, and Microsoft Foundry requires version 2.1.248. Those providers cannot discover cloud sessions or sessions on other machines.
It matters most for anyone who plans to keep running auto mode after August 14, since that’s the setting that makes messages between sessions arrive without a prompt.
What builders should do next
Run /status in a Claude Code session to check whether it has a “Peer address” row. If it does, the session can send and receive messages. Run /list-agents (also available as /peers) to see which of your other sessions it can currently reach.
Set crossSessionInbound to hold to keep incoming messages from reaching Claude. An explicit hold retains them until an accept setting later applies. Setting it to refuse turns off incoming messages entirely. To require approval before a message leaves your machine, set isolatePeerMachines to true.
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