Anthropic cuts false biology-block rate for Fable 5 by 85%

Anthropic reduced false positives in Fable 5's biology safety filters by about 85%. Previously, nearly all biology-related queries were blocked and rerouted to the less capable Opus 5 model. Restrictions remain in place for sensitive dual-use topics like virology and toxicology.

Why it matters: This is a concrete data point on how AI labs tune the tradeoff between usability and biosecurity: overly broad filters push users toward weaker models and frustrate legitimate researchers, so precision improvements like this matter for both safety credibility and adoption. It also shows Anthropic drawing a harder line specifically around virology and toxicology rather than biology in general.