# For cache diagnostics, the API now stores a request's fingerprint only when the request includes the…

By Steven Van · 2026-09-09

Requests that send only the old beta header still work but store no fingerprint, so pair diagnostics with a null previous\_message\_id on the first turn.

The [Anthropic](<https://creatorstoolbox.com/tools/anthropic>) API now stores a fingerprint for [cache diagnostics](<https://platform.claude.com/docs/en/build-with-claude/cache-diagnostics>) only when a request includes the diagnostics object. A request that sends just the cache-diagnosis-2026-04-07 beta header on its own is still accepted, but no fingerprint gets saved for it.

A later turn that points **previous\_message\_id** at one of those header-only requests now gets back **previous\_message\_not\_found** instead of a comparison. To avoid that, include the diagnostics object on every turn, passing "previous\_message\_id": null on the first one.

![Anthropic](<https://www.google.com/s2/favicons?domain=anthropic.com&sz=128>)

Anthropic

Anthropic is an AI safety and research company that's working to build reliable, interpretable, and steerable AI systems.

[View Anthropic →](<https://creatorstoolbox.com/tools/anthropic>)

[Original source](<https://platform.claude.com/docs/en/build-with-claude/cache-diagnostics>)

[Read For cache diagnostics, the API now stores a request's fingerprint only when the request includes the… on Creators Toolbox](<https://creatorstoolbox.com/blog/anthropic-for-cache-diagnostics-the-api-now-stores-a-request-s-fingerprint-only->)

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Canonical source: https://creatorstoolbox.com/blog/anthropic-for-cache-diagnostics-the-api-now-stores-a-request-s-fingerprint-only-