Users of Anthropic's Claude Code 2.1.236 have reported issues with the Fable 5 model, where it became unusable for certain tasks. The problem appears to stem from a hidden message inserted by Claude Code into Fable requests, which then triggers Fable's own safety classifier. This hidden message, intended to batch tool calls, is interpreted by the safety classifier as an instruction to surface internal reasoning, leading to a refusal rate of 18 out of 62 requests, compared to 1 out of 2,646 for requests without the message. Users have found that reverting to Claude Code 2.1.235 resolves the issue. AI
IMPACT This issue highlights potential conflicts between model versions and safety mechanisms, impacting usability and requiring users to revert to older versions.
RANK_REASON User-reported issue with a specific model version and its interaction with safety classifiers.
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