Anthropic cuts Fable 5's biology false positives by 85% by rewriting the classifier's constitution
Anthropic·high signal
Published August 7, Anthropic detailed how it loosened Fable 5's biology safeguards, which at launch routed flagged queries down to Opus 5 and generated frustrating refusals for legitimate clinical and educational use. Rewriting the classifier constitution — the rule set distinguishing safeguarded from allowed content — cut biology-related fallbacks ~85%, with total fallback reductions of 67% on Claude.ai, 55% on Cowork, 17% on Claude Code, and 7% on Claude Platform. Dual-use professional biology research and drug development remain blocked pending trusted-access pathways.