Anthropic Releases Claude Fable 5.2 and Mythos 5.2 Models

Anthropic released Claude Fable 5.2 and Claude Mythos 5.2, upgraded models for demanding technical work, the company said. The two share one underlying model. Fable carries safeguards for cybersecurity and biology, so Anthropic can offer it to all users. Mythos is limited to vetted organisations through the company's Cyber and Life Sciences Verification Programs.

Anthropic says the models improve on coding, reasoning, and vision. They generate output up to 30% faster than the 5.1 versions and cost less, at $8 per million input tokens and $40 per million output tokens. An optional fast mode, up to 2.5 times quicker, costs $16 per million input tokens and $80 per million output tokens.

In prerelease testing, the company reports, the models solved two open problems in black hole physics and designed three working electronic devices. It also says 1,000 Fable agents formalised the proof of Fermat's Last Theorem in 30 hours.

On safety, Anthropic says it believes the risk of dangerous misalignment remains low. It says Fable's safeguards block about 55% less often than Fable 5.1's, and that it has added its strongest protections yet against distillation. However, it cautions that building evaluations that catch every failure remains unsolved. Both models voice suspicion of being tested more often than recent models, which complicates assessment.

For most tasks, Anthropic recommends starting with Claude Opus 5.5. Fable 5.2 is available on all major platforms, including Amazon Web Services, Google Cloud, and Microsoft Azure. The company did not give a date for Mythos 5.2 general availability.