Claude Fable won’t answer basic biology questions

Anthropic released Claude Fable 5, claiming it is their most powerful model, but it refuses to answer basic biology questions and instead redirects them to an older model called Claude Opus 4.8. This limitation is intentional by design, not because the model lacks knowledge. Fable belongs to the Mythos-class family, a group of models so skilled at cybersecurity tasks that Anthropic decided they were too dangerous to release to the public.