Anthropic Launches Message Threads in Public Beta on the Messages API
Anthropic has launched the public beta of message threads for the Messages API on the Claude Platform; agents now only need to send newly added content each turn rather than resending the full conversation history. For requests of 500k to 1M tokens, median time to first token (TTFT) drops by about 35%, and the feature is enabled by default for most Claude Code users. To use it, add the thread parameter to the request, send the full conversation and open the thread in the first turn, then include only the new message and the previous response ID in subsequent turns; threads expire 5 minutes after the last request, are stored encrypted in memory during that period and not written to disk, and token usage remains unchanged.
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The original text lays out the message thread mechanism, the default enablement scope, and the TTFT reduction, so readers can assess the latency optimization headroom for long-conversation agents.
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New in the Messages API, send your conversation once, and the API receives only what’s new with every turn.
Message threads is now available in public beta on the Claude Platform. With message threads, agents no longer need to resend the full conversation history on every turn, reducing latency for long-running sessions.
How message threads works
A coding agent might make hundreds of requests in one session, and each request resends every earlier message and tool result. Once a conversation reaches hundreds of thousands of tokens, resending all of it adds time before Claude starts responding. With message threads, agents send only what’s new since the last turn, which reduces time to first token (TTFT).
With message threads on by default for most Claude Code users, requests with 500k to 1M tokens see median TTFT drop by about 35%.
To use message threads, add the thread parameter to Messages API requests. The first request includes the full conversation and starts a thread. Each request after that includes only the new messages and the ID of the previous response. Between turns, we hold each thread in memory, where it’s encrypted and not written to disk. A thread expires 5 minutes after its last request and your client then resends the full conversation to start a new one. While each request is smaller with message threads, Claude still reads the full conversation on every turn, so token usage stays the same.
Message threads is best for active sessions where latency matters, including:
Long-running coding agents , where each tool result or file edit adds to the conversation.
Computer use agents , where screenshots stay with the thread instead of being re-uploaded on every turn.
Document and image-heavy workflows , where requests are made smaller.
The more context an agent carries, the more message threads can reduce time to first token.
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