Anthropic launches Claude Fable 5.1 and Mythos 5.1
Anthropic is splitting Claude 5.1 into a broadly available Fable model and a restricted Mythos variant for higher-risk expert work.
Fable 5.1 is available through the Claude API, Anthropic products, AWS, Google Cloud, and Azure; Mythos is limited to vetted cyber defenders and life scientists. Anthropic says cache reads are now 75% cheaper, with typical costs down 25% and highly agentic work down about 45%. The company also says the new safeguards reduce false-positive cyber and biology interventions, while Enterprise Frontier Safeguards will phase in later this fall. Mythos posted stronger science and cyber benchmarks than Fable in some tests, and access is routed through Anthropic’s verification programs. TestingCatalog's note
Fable 5.1 is available through the Claude API, Anthropic products, AWS, Google Cloud, and Azure; Mythos is limited to vetted cyber defenders and life scientists. Anthropic says cache reads are now 75% cheaper, with typical costs down 25% and highly agentic work down about 45%. The company also says the new safeguards reduce false-positive cyber and biology interventions, while Enterprise Frontier Safeguards will phase in later this fall. Mythos posted stronger science and cyber benchmarks than Fable in some tests, and access is routed through Anthropic’s verification programs. TestingCatalog's note
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