Claude API adds message threads in beta: the server keeps the conversation, later requests send only new messages
Anthropic added message threads to the Messages API, in beta behind a beta request header. The conversation is kept on the server, so each later request sends only the new messages, which makes requests smaller and the first token arrive sooner. A thread expires 5 minutes after its last request and is deleted no more than 1 hour after its last use.
Why it matters
Developers running long conversations or agent loops no longer have to resend the whole history each time, so requests get smaller and faster.
Sources1
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