Claude Fable 5.1 and Claude Mythos 5.1

Claude Fable 5.1 and Claude Mythos 5.1 are the same AI model with different safeguard tiers; Fable 5.1 is generally available at roughly 25% lower cost than its predecessor, while Mythos 5.1 is restricted to trusted-access programs for cybersecurity and life-science work. Both incorporate Enterprise Frontier Safeguards that enforce zero data retention and cut false-positive rates by 60% in cybersecurity, and they outperform prior versions in coding, knowledge work, and scientific research, including identifying a long-standing software crash and supporting molecular-design projects.