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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.

← All of v2.1.251 Home All releases ←olderv2.1.250
Claude Code v2.1.251

Short model names no longer resolve to disallowed models

You'll notice
Useful3 Signal3
Models

Short names like opus or sonnet can no longer resolve to a disallowed model.

What

Matching a short name such as opus, sonnet, haiku or fable to a full model now refuses candidates that fail an allowed-base-model check, narrowing what these aliases can pick.

Details
  • The check runs first, before any name comparison, and is not configurable.
Evidence

if (Bm(r) && !Mw(r)) return !1;

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 v2.1.251 →