From the source
Anthropic introduced message threads in public beta on November 2, 2026, letting Messages API applications on the Claude Platform send only new messages after an initial full-conversation request.
- The feature targets active sessions where latency matters, including long-running coding agents, computer-use agents whose screenshots remain with the thread, and document- and image-heavy workflows.
- Anthropic reports that, with message threads on by default for most Claude Code users, requests containing 500,000 to 1 million tokens see median time to first token fall by about 35%.
- Claude still reads the full conversation on every turn, so token usage is unchanged and standard token rates and existing rate limits apply.
- Threads are best-effort and expire five minutes after their last request, and applications must keep their own copy of every message because there is no API to list, read or delete threads.
- Thread contents are held in memory under server-managed encryption, never written to durable storage, and deleted no more than one hour after last use; they are not eligible for zero data retention or HIPAA use.
- The beta is available on the native Claude Platform, Claude Platform on AWS, Claude in
Microsoft Foundry, and Claude Models on
Google Cloud under Anthropic management, with beta support on every model.