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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

Subagent model resolution now records where the model came from

Under the hood
Useful2 Signal2
Subagents

Subagent model choice now records where the model came from, not just its name.

CLAUDE_CODE_SUBAGENT_MODEL
What

Picking a subagent's model now tracks the source of the request separately from the model name, distinguishing tool overrides, the agent's own frontmatter, the CLAUDE_CODE_SUBAGENT_MODEL environment variable, and defaults.

Details
  • The existing model-resolution telemetry gained outcomes for a model family alias being stepped down, an override being dropped, and a family mismatch.
  • Aimed at correctness of which model a subagent ends up on; nothing new is surfaced in the UI.
Evidence

subagent_model_resolve

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 →