Fewer Switches to Opus 5 for Biology Queries

Fable 5 reduces biology-related fallbacks to Opus 5 by 85% while keeping restrictions in place for sensitive dual-use requests.

Fable 5’s biology safeguards have been adjusted to reduce blocks on queries that are incorrectly classified as sensitive. According to Anthropic’s testing, biology-related fallbacks to Opus 5 have decreased by about 85% across its products.

Common questions involving health, lab result interpretation, symptoms, or biology education should therefore remain on Fable 5 more often. Anthropic also says healthcare professionals will be able to use the model for a broader range of clinical tasks.

Requests considered dual-use are still redirected to Opus 5. This includes certain work in virology, toxicology, and molecular design. Fable 5 therefore remains restricted for parts of professional biology research and drug development while Anthropic works on controlled-access pathways.

To reduce false positives, Anthropic rewrote the rules used by its biology classifier, which relies on smaller systems to identify sensitive requests. New training data was then created, followed by retraining and evaluation with internal and external experts.

The company estimates that the change should also reduce fallbacks overall, regardless of cause, by about 67% on Claude.ai, 55% in Cowork, 17% in Claude Code, and 7% on Claude Platform. Anthropic notes that some false positives will still remain.