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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 v2.1.247 Home All releases ←olderv2.1.246 v2.1.248newer→
Claude Code v2.1.247

A model-capability toggle, tengu_willow_tern

Not switched on
Useful2 Signal5
Model Config Notable not in their notes

A new toggle applies only to models advertising an opus 5 prompt bundle capability.

tengu_willow_tern gates behaviour for models with the opus_5_prompt_bundle capability and compiles off; CLAUDE_CODE_WILLOW_TERN overrides.

Feature flag
tengu_willow_tern Off in both readings

The flag server returned off for the account this site reads and for the anonymous baseline. A reading of off cannot rule out a rollout these two readings sit outside of.

This account: off · anonymous baseline: off · compiled default in v2.1.247: not a boolean we can read

Read once, for one account on one subscription tier, against v2.1.247. It isn't a statement about your account. What a flag value here can and cannot tell you

CLAUDE_CODE_WILLOW_TERNtengu_willow_tern
What

A new toggle that applies only to models advertising the opus_5_prompt_bundle capability. It reads CLAUDE_CODE_WILLOW_TERN first, then a boolean tengu_willow_tern key in client data, then the flag, whose compiled fallback is off.

Details
  • Non-boolean client-data values are ignored, with a warning logged once.
  • What the toggle switches on beyond the prompt bundle is not evident from the added code.
Evidence

tengu_willow_tern

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 v2.1.247 →