Mythos 5.1 is also launching in Project Glasswing.

Mythos 5.1 is also launching in Project Glasswing.

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 on cached data that was already processed and stored.

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.

Anthropic says it’s “now allowing Fable 5.1 to be used for identifying software vulnerabilities,” but it will still redirect some cybersecurity tasks to Opus models, like “penetration testing, exploit generation, and binary-based vulnerability scanning.” Claude Fable 5.1 is now available on all platforms, while Mythos 5.1 is available to Project Glasswing participants only.