Anthropic describes Claude Fable 5.1 and Mythos 5.1 as the same underlying model with different safeguards and access arrangements. In its announcement, Fable is generally available, while Mythos is restricted to trusted access programs designed for cybersecurity and life-sciences work. That distinction affects which tasks users may undertake: the announcement permits vulnerability discovery with Fable, while excluding exploit development. Choosing between the names therefore involves eligibility and permitted use as well as the model's capabilities.
