Anthropic has launched Claude Fable 5.2 and Claude Mythos 5.2, two releases built on the same underlying model for open-ended technical work. Fable applies cyber and biology safeguards and is now available across Claude’s platforms, Amazon Web Services, Google Cloud and Microsoft Azure. Vetted cybersecurity and life sciences organizations can apply for Mythos through Anthropic’s verification programs, while developers can access Fable as claude-fable-5-2 on the Claude Platform.
The models target coding, scientific research, hardware engineering, robotics and complex analysis. Anthropic says they generate output up to 30% faster than Fable and Mythos 5.1 at a lower standard price of $8 per million input tokens and $40 per million output tokens. An optional fast mode raises generation speed by up to 2.5 times at $16 per million input tokens and $80 per million output tokens. Fable 5.2 scored 49.1% on FrontierCode 2.0 at Xhigh effort, while Mythos 5.2 reached 89.6% on Anthropic’s CVE Rediscovery evaluation.
Anthropic reports that Fable 5.2 solved two open problems in black-hole physics, coordinated about 1,000 agents to formalize Fermat’s Last Theorem in 30 hours, and designed three working electronic devices whose boards required no electrical modifications. It also scored 64.9% on the RoboDojo Sim robotics test. Mythos 5.2 accurately modeled 28 of 34 attempted AAV capsids by combining predictions for overlapping groups of protein chains with known capsid symmetries.
Anthropic positions Opus 5.5 as the starting point for most daily coding and knowledge work, with Fable or Mythos reserved for the hardest projects and Sonnet or Haiku for lighter tasks. Fable can also advise smaller models or orchestrate their work.
More than 90% of changes merged into Anthropic’s core codebase are now written by Claude with human guidance, and early users including Vercel, Shopify and Datadog described Fable 5.2 as especially capable on ambiguous engineering work. Anthropic says predeployment testing found low high-stakes misalignment risk, while Fable’s safeguards produced about 55% fewer blocks than Fable 5.1 in early testing.
Sources and related context #
- Claude Fable 5.2 model documentation : Supports: Anthropic's model page confirms the claude-fable-5-2 API ID, standard pricing, and verified access for Mythos 5.2.