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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.237

System prompt caching now requires a recognised endpoint

You'll notice
Useful4 Signal3
Prompt Caching Notable

If you point Claude at a proxy or custom gateway, the system prompt is no longer cached.

ANTHROPIC_BEDROCK_BASE_URLANTHROPIC_VERTEX_BASE_URLANTHROPIC_BEDROCK_MANTLE_BASE_URLANTHROPIC_FOUNDRY_BASE_URL
What

The check deciding whether the system prompt block may be marked cacheable used to only require that experimental betas were not disabled. It now also requires a known provider and endpoint: Bedrock, Vertex and Mantle qualify only when ANTHROPIC_BEDROCK_BASE_URL, ANTHROPIC_VERTEX_BASE_URL and ANTHROPIC_BEDROCK_MANTLE_BASE_URL are unset, and Foundry only when ANTHROPIC_FOUNDRY_BASE_URL is unset or its hostname ends in .services.ai.azure.com. Behind a proxy or custom gateway, the system block stops being cached.

Details
  • First-party and Anthropic-on-AWS paths still have to pass the existing beta and base-URL checks.
  • No feature flag; the outcome is decided entirely by the provider and those environment variables, and it is live for everyone on this build.
Evidence

.services.ai.azure.com

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.237 →