Make long-running agents faster with message threads

From the source

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.

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