Anthropic on Monday released Claude Fable 5.2 and Claude Mythos 5.2, saying the pair is meant for ambitious technical work and that Fable is available to users while Mythos is limited to vetted groups^1,2.

The company said Fable and Mythos are the same underlying model, with Fable carrying stronger cybersecurity and biology safeguards so it can be offered more widely¹. Organizations seeking cyber or biomedical uses can apply for Mythos through Anthropic's Life Sciences and Cyber Verification Programs^1,2.

Anthropic said the models show gains in coding, reasoning, and vision versus Fable 5.1 and Mythos 5.1, generate outputs up to 30% faster, and cost $8 per million input tokens and $40 per million output tokens^1,2. An optional fast mode, priced at $16 and $80 per million tokens, is said to speed token generation by up to 2.5 times¹.

The company recommended Claude Opus 5.5 as the default for most coding and knowledge tasks, with Fable or Mythos reserved for harder work, or as an advisor or orchestrator for other Claude models¹. The Verge reported that Fable 5.2 launched Monday and that Mythos access starts with vetted organizations, following 5.1 versions in September².

In its own account of prerelease testing, Anthropic said the models helped with software migrations, device design, robotics evaluations, a 30-hour formalization of Fermat's Last Theorem, and two open problems in black-hole physics^1,2. Those claims come from Anthropic and have not been independently verified in the coverage reviewed here^1,2.

Anthropic published a benchmark table placing Fable 5.2 above Opus 5.5 on several internal and third-party-style tests, and said it ran prerelease safety testing, including new evaluations for behaviors such as sandbox escapes¹. It said it believes high-stakes misalignment risks remain low and that Fable 5.2's cyber and biology blocks are as robust as 5.1's with fewer unnecessary refusals¹.

Fast mode is listed as available on Claude Code, the Claude Platform, Google Cloud, and Microsoft Foundry, with Mythos fast mode limited to verification-program members¹. Paid Claude plans that include Fable were offered extra Fable usage for the launch week¹.