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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 v2.1.242

Opus 5 disabled-thinking advice merged into one instruction

You'll notice
Useful2 Signal3
Model Docs

Advice for running Opus 5 without thinking is now a single combined instruction instead of two.

What

The guidance for running Opus 5 with thinking turned off previously gave separate fixes for two problems: a tool call written out as plain text that silently never runs, and internal thinking tags leaking into the answer. They are now one combined instruction.

Details
  • The combined rule allows a preamble sentence, tells the model to say so when no available tool fits the request, and forbids internal XML tags in general rather than naming a specific tag.
  • The existing rule against naming thinking tags in the prompt is kept and restated in the checklist.
Evidence

If no tool can express what the user asked for, say so instead of guessing.

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 v2.1.242 →