In a moment that marks a quiet but significant threshold in the history of artificial intelligence, Anthropic has disclosed that it detected and halted research on its platform that it could not confirm as either legitimate science or weapons development. Faced with irreducible uncertainty at the intersection of AI capability and biosecurity risk, the company chose precaution over access. The incident asks a question that no algorithm can yet answer: when the tools of healing and the tools of harm are identical, how does any institution — human or machine — learn to tell them apart?