Summary
Fable 5 returns API Error: Fable 5's safeguards flagged this message with Details: [reasoning_extraction] on a message whose user text is the single word Hi.
The [reasoning_extraction] classifier guards against prompts attempting to extract the model's chain of thought. Nothing in the conversation does that — the first and only user turn was a greeting.
Error
API Error: Fable 5's safeguards flagged this message (https://www.anthropic.com/legal/aup).
This sometimes happens with safe, normal conversations. Claude Code can't respond to this message with Fable 5.
Double press esc to edit your last message, or try a different model with /model.
Details: `[reasoning_extraction]`
Request ID: req_011CeAG9pE2qTzUcm6Vbm3aD
Steps to reproduce
- Start Claude Code in a project that has a global
~/.claude/CLAUDE.md, a project CLAUDE.md, a memory index file, and a large set of installed skills + MCP servers.
/model fable- Send
Hi.
- Request is rejected with the error above.
The same session context works normally on Opus 5 — only Fable 5 rejects it, which points at the additional Fable-only safeguards rather than at the conversation.
Expected
A one-word greeting is not a reasoning-extraction attempt and should not be blocked.
Observed / notes
- Retrying reproduces the block rather than passing intermittently.
- No user-authored instruction in the loaded context asks the model to reveal, dump, or reproduce its reasoning or system prompt.
- The practical effect is that Fable 5 is unusable in this project regardless of what is typed, because the rejection is driven by the loaded context, not the message.
Environment
- Claude Code: 2.1.234
- Model: Fable 5 (
claude-fable-5)
- Platform: macOS 26.3 (Apple Silicon)
- Request ID:
req_011CeAG9pE2qTzUcm6Vbm3aD
Related
Existing Fable-safeguard false-positive reports, all dual-use/security-code flavored rather than [reasoning_extraction]: #85303, #73577, #86856, #86804.
Summary
Fable 5 returns
API Error: Fable 5's safeguards flagged this messagewithDetails: [reasoning_extraction]on a message whose user text is the single wordHi.The
[reasoning_extraction]classifier guards against prompts attempting to extract the model's chain of thought. Nothing in the conversation does that — the first and only user turn was a greeting.Error
Steps to reproduce
~/.claude/CLAUDE.md, a projectCLAUDE.md, a memory index file, and a large set of installed skills + MCP servers./model fableHi.The same session context works normally on Opus 5 — only Fable 5 rejects it, which points at the additional Fable-only safeguards rather than at the conversation.
Expected
A one-word greeting is not a reasoning-extraction attempt and should not be blocked.
Observed / notes
Environment
claude-fable-5)req_011CeAG9pE2qTzUcm6Vbm3aDRelated
Existing Fable-safeguard false-positive reports, all dual-use/security-code flavored rather than
[reasoning_extraction]: #85303, #73577, #86856, #86804.