September 9, 2026 · Anthropic

Cache diagnostics store request fingerprints only when diagnostics object is sent

For cache diagnostics, the API now stores a request’s fingerprint only when the request includes the diagnostics object. A request that sends only the cache-diagnosis-2026-04-07 beta header is still accepted, but no fingerprint is stored. A later turn that points previous_message_id at it reports previous_message_not_found. Include diagnostics on every turn, with "previous_message_id": null on the first.