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Messages API adds on-demand conversation compaction in beta

BetaVerifiedAdded 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.

Topics: LLMs, Developer tools

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