Claude API launches message threads in beta for smaller requests

Message threads keep the conversation on the server, so each later request sends only the new messages. A thread expires 5 minutes after its last request and is deleted no more than 1 hour after last use.

Who is affected:

Developers running long conversations and agent loops on the Messages API can cut request size and time to first token.

What to do:

Try the message-threads-2026-08-12 beta header on long-running conversations.