Claude Fable 5 vs Mythos 5: What’s the Difference?
Fable 5 and Mythos 5 share the same underlying model — the difference is who can use it and which safeguards are in place.
Fable5Anthropic launched two models on the same day: Claude Fable 5 and Claude Mythos 5. They share the same underlying Mythos-class model — what differs is the audience and the safeguards.
Claude Fable 5 — public, safeguarded
Fable 5 is generally available. It ships with safeguards so it’s safe for everyone to use. On a narrow set of high-risk topics — such as cybersecurity and biology — it quietly routes the response to Claude Opus 4.8 instead. On average this fallback triggers in fewer than 5% of sessions.
Claude Mythos 5 — restricted, unrestricted
Mythos 5 is the same model with safeguards lifted in some areas. Because of that, access is limited to a small group of vetted cyberdefenders and infrastructure providers — the people who need the model’s full capabilities to defend systems at scale.
Why split them?
The split lets Anthropic release a frontier-level model to the public without handing every capability to everyone. Fable 5 gives developers Mythos-class reasoning with guardrails; Mythos 5 gives trusted defenders the unrestricted version.
Safety testing
Both went through extensive red-teaming — over 1,000 hours — with no universal jailbreak discovered.