Message Threads
Anthropic's beta Messages API feature that keeps conversation state server-side so clients send only new messages.
Overview
Anthropic opened Message Threads as a public beta of the Messages API on November 2, 2026. After one full-conversation request, clients send only new messages while the server keeps state between turns. Threads are best-effort and expire five minutes after the last request, and a lost thread returns 404 thread_not_found, so apps must keep their own copy of the conversation. Anthropic reports about 35% lower median time to first token for requests of 500K to 1M tokens, and threads are on by default for most Claude Code users.
This is a sourced directory entry. Features and capabilities are reported in the linked sources; this entry does not document independent Aymorphic testing.
Key features
- Send only new messages after the first full request
- Beta header message-threads-2026-08-12; SDK helper client.beta.messages.thread()
- Threads expire five minutes after last request; 404 thread_not_found on loss
- About 35% lower median time to first token for 500K-1M token requests (Anthropic-reported)
- Not supported with Message Batches, token counting or most context editing; unavailable with Inference hooks
- Available on Claude Platform, Claude Platform on AWS, Claude in Microsoft Foundry and Claude Models on Google Cloud
Use cases
- Long-running coding or research agents with very large contexts
- Cutting request payload size for chatty multi-turn clients
Pricing
Billed per token at standard rates; billing still counts the full context processed.
Pricing reflects the source record and may change. Confirm current terms with the provider.
Dates and sources
- Released
- 2 Nov 2026
- Record updated
- 7 Nov 2026
- Record last checked
- 7 Nov 2026