# Anthropic releases Claude Fable 5.1 and Mythos 5.1 > Source: > Published: 2026-09-02 15:23:49+00:00 # Anthropic releases Claude Fable 5.1 and Mythos 5.1 Anthropic has released Claude Fable 5.1 and Mythos 5.1, addressing issues such as performance, data retention, safeguards and price. The updates also target scientific discovery, as the company tested the capabilities of the models across many domains. Internal testing shows that Fable 5.1 outperforms Fable 5 when is comes to coding, knowledge work and problem-solving tasks, the company said. And in low or medium effort tests, the results are similar but at a much lower cost. Craig Falls, Head of Quantitative Research at Jane Street Capital, said in a statement: “In internal benchmarks, Claude Fable 5.1 solves more of our coding problems than Fable 5 or Opus 5, and achieves state of the art on trading intuition. While prior models became hard to follow the longer they worked, Fable 5.1 remains readable over long, multi-step tasks.” When it comes to safeguards, the company’s Enterprise Frontier Safeguards (EFS) provide the kind of privacy that’s equal to a zero data retention policy, and able to prevent malicious use. The safeguards store data in cloud infrastructure that an organization completely controls. This capability will be available beginning later this fall, the company said. The two model updates are the same, but differ in terms of safeguards. While Fable 5.1 is available for general use, Mythos. 5.1’s safeguards are designed specifically to support cybersecurity and work in life sciences. The updated safeguards reduce the amount of alerts where the system flags content that’s benign. Anthropic also noted that the new safeguards block 60% fewer false positives than before. Claude Fable 5.1 and Claude Mythos 5.1 are the same model, but with different levels of safeguards. Fable 5.1 is generally available, while Mythos 5.1 is available only through our trusted access programs; its safeguards are specifically designed to support work in cybersecurity and the life sciences. According to the company, based on token usage, Fable 5.1 is expected to be about 25% less expensive that Fable 5. That, the company said, has been accomplished by lowering the pricing on cache reads — inputs previously processed and stored. It also said highly agentic work will be up to about 45% less costly. To learn more about the scientific advancements of these updated models, read Anthropic’s [announcement blog](https://www.anthropic.com/claude-fable-and-mythos-5-1).