Anthropic launches Claude Fable 5.1 and Mythos 5.1 for coding and research
Anthropic announced (Sept 1) Claude Fable 5.1 and Claude Mythos 5.1—the same underlying model with different safeguards—as its most advanced models for coding and knowledge work. Fable 5.1 is generally available via `claude-fable-5-1` on the Claude API plus AWS, Google Cloud, and Microsoft Azure at $10/$50 per M input/output tokens, with cache reads cut 75% to $0.25 per M (~25% lower typical cost, up to ~45% for highly agentic workloads). Mythos 5.1 keeps more permissive cyber/life-sciences safeguards for vetted U.S. trusted-access programs. Reported gains include Terminal-Bench-Science 52.6% (vs 24.7% Fable 5), Terminal-Bench 4.0 55.8% / 60.9% Mythos, plus early scientific results (high-affinity protein binders, a higher-resolution Venus DEM, GPU kernel speedups). Anthropic also previewed Enterprise Frontier Safeguards (customer-controlled ZDR-style monitoring rolling out later this fall) and an EU AI Act watermark detection API in private preview. Distinct from Fable 5 biology-safeguards updates and from Aug 31 alignment/security hardening.






