Anthropic’s new Fable release is cheaper

Anthropic says its newest AI models, Fable 5.1 and Mythos 5.1, address criticisms from customers about price, data retention, and overzealous safeguards. The company claims Claude Fable 5.1 offers stronger performance than Fable 5, but costs around 25 percent less typically and up to 45 percent less for complex agentic tasks, thanks to reduced pricing […]. Anthropic launches Claude Fable 5.1 and says it’s up to 45 percent cheaper for agentic work.

Mythos 5.1 is also launching in Project Glasswing. Along with the announcement, a slew of early impressions popped up, including from Every CEO Dan Shipper, who claims, “It’s the strongest coding model we’ve used, but now it’s fast, token-efficient, and crucially actually speaks like a normal person.” Box CEO Aaron Levie is another early access believer, saying that his company’s agent with Fable 5.1 picked up on subtleties and ambiguities in data that Fable 5 missed in the same test. Meanwhile, Lisan al Gaib points out that on benchmarks, Mythos 5.1 with low reasoning scores the same as its predecessor set to Max reasoning.

Fable 5.1 also has “more precise safeguards” that Anthropic says are less likely to block basic biology questions than Fable 5, but Mythos 5.1 has the same biology restrictions as the previous model. Anthropic also explained its progress on data retention, saying that Enterprise Frontier Safeguards offer “complete privacy” by storing data on the customer’s cloud servers instead of its own, and will start rolling out later this fall.

Fable 5.1 includes changes meant to reduce token cost and false-positive restrictions from the model's safeguards. Anthropic’s new Fable release is cheaper, less restrictive.

As with the previous Mythos model, Mythos 5.1 will only be available to registered Anthropic partners engaged in either cybersecurity or life sciences research. Fable 5.1, the unrestricted version, is available starting today on cloud platforms or through the Anthropic API.

One of the most significant changes is Anthropic’s previously reported embrace of zero data retention, allowing clients to run Anthropic models on their own infrastructure without data outflows. Previously unavailable for Fable due to security concerns, a high-privacy service (called Enterprise Frontier Safeguards) will now roll out to users in the fall.

The system will still monitor for misuse by agents or human users, but clients will control how the monitoring takes place. As part of the announcement, Anthropic assured customers that their data had not been inappropriately accessed.

“Anthropic has never trained on enterprise data without explicit permission, and never will,” the announcement reads.