Sending a message to another agent via send_message now checks whether that agent has been stopped but hasn't finished settling. If so, the send is refused with a dedicated error instead of proceeding against an agent mid-stop.
Names in the bundlesend_message
Documented inapi/agents-and-tools/tool-use/define-tools
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up send_message, on Agent SDK reference - TypeScript.
* `peer-send-message`: the notification is a message that another of your sessions sent with the server-side `send_message` tool that [cloud sessions](/docs/en/claude-code-on-the-web) use to message each other, not the [cross-session `Send…agent-sdk/typescript see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up send_message, on Agent SDK reference - TypeScript.