In June, Anthropic first released Fable 5, its Mythos-class AI model for Claude. Three months later, Anthropic is improving Claude with its new Fable 5.1 model update. Claude Fable 5.1 and Mythos 5.1 arrive today In the world of Anthropic, Fable is Claude’s most capable model. Haiku, Sonnet, and Opus are the small, medium, and large models under Fable. “Claude Fable 5.1 sets a new standard in coding, knowledge work, and long-term problem-solving tasks,” says Anthropic. The company says the new model has a higher level of performance compared to Fable 5. Anthropic also says that Fable 5.1 “achieves similar or better results than Fable 5 at a much lower cost” when configured with low or medium effort. More from Anthropic below: Fable 5.1 avoids shortcuts that result in poorer quality work and is smart enough to fix the root causes of software problems. For example, in testing by investment firm Millennium, Fable 5.1 found the cause of a rare glitch in its internal systems that none of its engineers (or any other model) had been able to explain after several years of trying. In addition to Fable 5.1, Anthropic is also releasing Mythos 5.1 for users with access to Mythos. “Claude Fable 5.1 and Claude Mythos 5.1 are the same model, but with different levels of protection,” Anthropic explains. “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 life sciences.” Here’s the pricing data for Fable 5.1: Fable 5.1 will cost about 25% less than Fable 5 for typical workloads, as long as usage is billed via token. This is because we are reducing our prices on cache reads (where the model reads entries that have already been processed and stored). For highly agentic jobs, the savings are typically much higher: up to about 45%. In terms of pricing, Anthropic says it has “reduced the price of Fable 5.1 cache reads (where the model reuses the context it has already processed) where usage is billed per token, like in our API.” The company says this “leads to a substantial reduction in the overall cost of running the model.” The price is otherwise unchanged from Fable 5. You can find out more in the announcement post here. FTC: We use automatic affiliate links that generate income. Further.
