Anthropic Launches Claude Fable 5.2 and Mythos 5.2
Anthropic announced Claude Fable 5.2 and Claude Mythos 5.2 on November 9, 2026, successors to the 5.1 models from September 2026. Fable 5.2 improved on FrontierCode 2.0 from 32.4% to 49.1% and on Humanity's Last Exam from 65.6% to 74.2%.
2 sources 3h ago
Reporting from 2 sources: ASCII.jp, GIGAZINE.
Why it matters
The OS experiment is the concrete claim behind the autonomy pitch: Fable 5.2 was given a rough instruction and ran design, coding, testing, and review across more than 1,000 agents without a human stepping in, which is a different scale of task than code generation and fixing.
Key Facts
- Anthropic announced Claude Fable 5.2 and Claude Mythos 5.2 on November 9, 2026.
- Claude Fable 5.2 improved from 32.4% to 49.1% on FrontierCode 2.0 and from 65.6% to 74.2% on Humanity's Last Exam.
- In an Anthropic engineer experiment, Fable 5.2 commanded over 1,000 auxiliary AI agents for 8 days and completed an OS that boots on a laptop.
- Claude Mythos 5.2 is provided only to organizations that pass screening.
- API usage fees for the new models fell 20%, from $10 to $8.
In an Anthropic engineer experiment, it directed over 1,000 auxiliary AI agents for 8 days and completed an OS that boots on a laptop.
Fable 5.2 and Mythos 5.2 share a base model but split on access. Fable carries safety measures against misuse in cybersecurity and biology. Mythos has fewer restrictions and is provided only to organizations that pass screening.
Anthropic also reported that Fable 5.2 coordinated 1,000 AI agents to convert the proof of Fermat's Last Theorem into a computer-verifiable format in about 30 hours, and that it designed three electronic devices, including a voice assistant device and a USB speakerphone, that work. Output speed is up to 30% faster than the old models, and API fees fall 20%, from $10 to $8 per unit.
Written with AI by Yomimono from the 2 cited sources below, including Japanese-language reporting where cited. See our editorial policy.
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