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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 v2.1.219

Armed fallback model must belong to the same family

You'll notice
Useful3 Signal0
Models

Fallback model only kicks in when it truly matches the model you asked for.

What

The armed fallback model is only used when it genuinely matches the target, instead of being pushed through a remapping helper first.

Details
  • The remapping helper call is gone from this path.
  • The fallback is used only when its normalised family matches the mapped target's family and it has not already been tried.
  • Otherwise the code falls through to the regular resolution path.
Evidence

armedFallbackModel

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 v2.1.219 →