Claude Code: Cross-Session Messaging Between Independent Instances

ArticleAnthropicResource

Anthropic details cross-session messaging in Claude Code, enabling independent CLI sessions to share findings, coordinate parallel git worktrees, and request idle notifications across local and remote environments.

Key points

  1. Requires Claude Code v2.1.224 or later on macOS/Linux and v2.1.234 or later on Windows; enabled automatically without manual configuration.
  2. Claude relies on ListAgents to discover available sessions and SendMessage to route text messages between them.
  3. Messages transmit plain text only; permissions stay strictly isolated per session and cannot be bypassed by proxying requests.
  4. Users can target specific sessions using @-mentions in prompts, supported by typeahead completion for local instances.
  5. A notify_when_idle option lets one session subscribe to a one-time notification when another long-running session finishes or exits.
  6. Inbound controls allow sessions to set message policies to delivered, held, or refused.

Why it matters

Developers increasingly run multiple concurrent AI coding sessions across separate git worktrees or remote machines. Cross-session messaging removes the manual overhead of copy-pasting context and status updates between terminals.

Analysis

With cross-session messaging, Anthropic introduces a lightweight coordination mechanism for multi-session development without forcing heavy orchestration architectures. Crucially, the protocol enforces strict session boundaries: tools refuse messages aimed at escalating denied permissions, and safety checks on local inbox sockets protect against malicious processes and symlink attacks.

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Summary generated by AI (Gemini 3.8 Flash, 27 September 2026). It may contain errors – the original source is authoritative.

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