Anthropic unveils Claude Fable 5.1 and Mythos 5.1 for coding and knowledge work

Artificial intelligence company Anthropic announced the launch of Claude Fable 5.1 and Claude Mythos 5.1, describing them as the world's most advanced models for coding and knowledge work.

Artificial intelligence company Anthropic announced the launch of Claude Fable 5.1 and Claude Mythos 5.1, describing them as the world's most advanced models for coding and knowledge work. According to Anthropic, both offerings represent the same underlying model architecture but feature different tiers of operational safeguards. The company stated that Claude Fable 5.1 is generally available to users, whereas Claude Mythos 5.1 is restricted to trusted access programs with protections configured specifically for cybersecurity and life sciences research.

"They're the world's most advanced models for coding and knowledge work--and their research capabilities offer an early glimpse of how AI models will contribute to scientific progress," Anthropic said in an official statement. The company reported that Claude Fable 5.1 delivers higher performance than its predecessor, Fable 5, across long-running problem-solving and technical tasks. Anthropic noted that when operated under Low or Medium effort parameters, Fable 5.1 delivers comparable or superior outcomes at reduced computational expenses.

"Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads, wherever usage is billed by token. This is because we're reducing our pricing on cache reads," Anthropic stated. The organization further noted that, "For highly agentic work, the savings will often be much larger--up to approximately 45%."

In practical evaluations conducted by the investment firm Millennium, the system identified the source of an intermittent internal crash that human engineers and earlier models failed to resolve over several years. On data privacy, Anthropic outlined a framework titled Enterprise Frontier Safeguards (EFS), which retains customer information within customer-managed cloud infrastructure rather than company-owned servers. Rollouts of EFS for enterprise accounts are scheduled to commence in phases later this fall, with interim provisions granting zero data retention to eligible users.

"In cybersecurity, our newest safeguards block 60% fewer false positives than before. In part, this is because Fable 5.1 can now be used to discover software vulnerabilities--though not to develop exploits for them," the statement read. On the pricing front, Anthropic stated that they have reduced the price of Fable 5.1's cache reads (where the model reuses context it has already processed) wherever usage is billed by token, such as on their API. Cache reads now cost 75 per cent less, or USD 0.25 per million tokens.

"This change leads to a substantial reduction in the overall cost of running the model. For typical workloads, costs are reduced by around 25% relative to Fable 5." The AI firm disclosed that Fable 5.1's pricing is the same as Fable 5's: $10 per million input tokens and $50 per million output tokens.

"In parallel, we're continuing our work to bring many of the improvements of Fable 5.1 to the rest of our model family. As discussed above, Claude Mythos 5.1 is available to vetted cyberdefenders and life scientists. Currently, it is only available to a set of US organizations, though we're coordinating with the US government to expand access to a broader set of domestic and international partners as quickly as possible," Anthropic said. (ANI)