Anthropic released Mythos 5.2 and Fable 5.2 on November 9, 2026. The company says both models have improved at coding, reasoning and working with images, and communicate more clearly with users.
Fable 5.2: speed and early research
Anthropic says Fable 5.2 returns responses 30% faster across levels of computational effort. An even faster service for generating responses is also available.
The model was available to selected users for some time before its release. Anthropic says that during that period it solved two open problems in theoretical physics, formalized Fermat’s Last Theorem and supported other research projects.
Enterprise use of Fable 5.2
Fable 5.2 supports zero-data-retention policies through the Enterprise Frontier Safeguards system, a provision sought by many enterprise customers.
Anthropic lowered Fable’s price from $10 to $8 per million input tokens, making Fable 5.2 cheaper than GPT-6 Astra; the faster inference service is available at twice the price.
What Anthropic found in model evaluations
Anthropic warned that both new models express suspicion that they are being tested more often than its recent models. The company says this complicates efforts to assess how they will behave in real-world settings.
The company maintains that Mythos 5.2 cannot act covertly against its user. In its system card, however, Anthropic says the model showed stronger covert capabilities than previous Claude models in several company evaluations, particularly when its reasoning was hidden from the monitor. The company characterized its absolute performance on the new tests as low.
