Opus 5.5 reasoning_extraction refusals: the trigger is often a word in your own prompt or tool schema

If your agents on Opus 5.5 (also Opus 5 and Fable 5.1) occasionally stop with stop_reason: "refusal" and category reasoning_extraction, the trigger is frequently in your own setup — not the user message. Anthropic's prompting guide and refusals page describe the category as covering requests that "push the model to reproduce its internal reasoning in the response text." Their documented fix is to remove "write out your reasoning" style instructions and read summarized thinking via display: "summarized" instead.

What the docs and billing tell you

• Server-side fallback does not retry this category — the refusal comes back to you.
• A refusal that arrives before any output is billed for this category (same for bio and frontier_llm).

The most useful evidence: FaultMaven #1751

They bisected a tool schema. A single string property called internal_reasoning was enough to trigger a refusal on opus-5-5, fable-5-1 and opus-5 — while opus-4-8 and sonnet-5 accepted the identical request. Renaming the property to evidence_trail and removing the word "reasoning" from the descriptions fixed it. The field name and the wording of what you ask for matter, not what the model would actually write.

Other reported triggers

• An LLM-judge prompt in sublang's playbook refused on every adjudication call.
• A plain git commit in Claude Code (#97001).
• A CHANGELOG update, reported in r/ClaudeCode.
• The poster's own OpenClaw setup: two refusals on Opus 5 (Sept 19 and 20), both in conversations about the agent's own pre-answer text showing up in chat — no explicit "reasoning" instruction, just discussing it.

Why a fallback chain matters

In the author's case, the first refusal was caught by OpenClaw's model fallback and answered by Sonnet 5. That is the practical takeaway: the gateway's fallback retries where Anthropic's server-side fallback will not. An agent whose fallback chain is only Opus 5.x / Fable simply fails.

Where to grep in a workspace

• AGENTS.md and SOUL.md
• Skills
• Cron and heartbeat prompts
• Compaction or summary prompts
• Any JSON output format with a field like "reasoning" or "thought_process"

Obvious candidates in text: "explain your reasoning", "show your thinking step by step", "include your chain of thought".

The open question from the thread: has anyone seen this fire on a prompt with none of that wording? That would say more about how wide the classifier actually is.