Unclear Whether the refusal fallback feature itself is switched on for everyone is not settled.
What
Claude Code keeps a list of which model to fall back to when the session's model refuses a request in a given category. For sessions on claude-opus-5-5, that list now includes the frontier_llm category, which falls back to claude-opus-5. Before, only the bio and cyber categories had fallbacks. The default list gains the same entry.
Why
If you use Opus 5.5 and hit this kind of refusal, Claude Code may now retry on Opus 5 instead of stopping at the refusal.
Names in the bundleclaude-opus-5-5claude-opus-5
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Added since
A small documentation edit on prompting-claude-opus-5-5 touched a line naming claude-opus-5-5 after this was published.
* **Reasoning extraction:** Requests that push the model to reproduce its internal reasoning in the response text may be declined with the `reasoning_extraction` category. If your prompts ask the model to write out its reasoning in the res…build-with-claude/prompt-engineering/prompting-claude-opus-5-5 see the edit
Added since
A small documentation edit on prompting-claude-opus-5-5 touched a line naming claude-opus-5 after this was published.
* **Reasoning extraction:** Requests that push the model to reproduce its internal reasoning in the response text may be declined with the `reasoning_extraction` category. If your prompts ask the model to write out its reasoning in the res…build-with-claude/prompt-engineering/prompting-claude-opus-5-5 see the edit
Confirmed since
Anthropic's documentation has since written up claude-opus-5-5, on advisor-tool.
| Claude Haiku 4.5 (claude-haiku-4-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opu…agents-and-tools/tool-use/advisor-tool see the edit
Confirmed since
Anthropic's documentation has since written up claude-opus-5, on advisor-tool.
| Claude Haiku 4.5 (claude-haiku-4-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opu…agents-and-tools/tool-use/advisor-tool see the edit
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
Whether the refusal fallback feature itself is switched on for everyone is not settled.
Anthropic's documentation agrees
Anthropic's documentation has since written up claude-opus-5, on advisor-tool.