Messages API adds on-demand conversation compaction in beta

BetaSep 14, 2026VerifiedAdded Sep 22, 2026

With the compact-2026-09-04 beta header, the top-level compaction parameter returns a signed compaction block summarizing prior messages, which you send in their place on later requests. You choose when to compact, it can run in the background, and recent turns can be kept verbatim.

LLMs Developer tools

Read Anthropic's release notes

https://platform.claude.com/docs/en/release-notes/overview#september-14-2026

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