You'll noticeTier: how much it should matter to you
1Useful: my rating, 1 to 5
2Signal: worth watching, 1 to 5
Multi-SessionArea: what it touches
ImprovementsKind: in v2.1.284,
ImprovementsSection of the release
What
When a message from another Claude session arrives in the middle of a turn, Claude Code adds a note to it. That note normally ends: "After completing your current task, decide whether/how to respond (reply via SendMessage to the from= address)."
A new sendMessageToolAbsent flag is set on queued messages from a peer (another Claude session) when the SendMessage tool is not available.
With the flag set, the note ends with just " After completing your current task, decide whether/how to respond."
In that case, messages injected by the host also keep their host-delivery wording.
The SendMessage tool's own description is unchanged.
Why
Claude is no longer told to use a tool it does not have in that session.
How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtWhich session setups leave the SendMessage tool unavailable is not stated.
Anthropic's release notes agreeFixed sessions launched without the SendMessage tool (such as by Claude Desktop) still being told to message other sessions with it
