Anthropic has released Claude Fable 5, the first publicly available model in its so-called Mythos class. Early tests show a major leap in coding performance, but safety filters, pricing, and data retention policies are drawing sharp criticism.
With Claude Fable 5, Anthropic has shipped a model that tops nearly every benchmark. Fable 5 is the first publicly available version of the "Mythos class." According to Anthropic, Fable shares its base model with Claude Mythos 5 but adds strict guardrails that block potentially harmful requests related to cybersecurity, biology, chemistry, and model distillation. Mythos 5 is also available but limited to a small group of users.
What "Mythos" actually means on a technical level is mostly guesswork. Every CEO Dan Shipper, whose team had early access, reports that Anthropic staff told him there's nothing special about the architecture. Within the Haiku, Sonnet, and Opus family, Mythos simply refers to the largest and most capable model. Developer Simon Willison suspects the same, that it's the biggest Anthropic model publicly available to date. Fable just feels "big," Willison writes, "not just in terms of speed and cost, but also in how much it knows." Artificial Analysis backs this up: on its AA-Omniscience knowledge and hallucination benchmark, Fable scores 40 points, seven more than the previous leader, Gemini 3.1 Pro. Among open-weight models, that kind of gap typically tracks with model size.
