Source Intelligence

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

Pending model switches now get an immediate reply and a follow-up

You'll notice
Useful2 Signal3
Model Switching

A model switch over the control bridge replies immediately as pending, then follows up with the result.

What

A model switch requested over the control bridge no longer has to resolve on the spot. If the verdict is still outstanding, the bridge replies at once that the switch is pending, waits up to 8 seconds, then sends a follow-up system notice saying the pending switch was applied or failed.

Details
  • The pending reply reads: "This model switch is still pending (an earlier model request or a PreModelSwitch hook has not finished); it will apply when that completes unless it is refused".
  • The follow-up is "The pending model switch was applied" or "The pending model switch failed".
  • The deadline can in principle be supplied per request, but nothing in the build sets it, so the built-in 8000ms default always applies.
  • Typical causes of a pending verdict are an earlier model request still in flight or a PreModelSwitch hook that has not returned.
Evidence

This model switch is still pending (an earlier model request or a PreModelSwitch hook has not finished); it will apply when that completes unless it is refused

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

See this entry in the whole of v2.1.251 →