Anthropic released Claude Fable 5.1 and Mythos 5.1, with the same base model but different railings.
Anthropic releases Claude Fable 5.1 and Mythos 5.1: both use the same basic model, with Fable being open to general users and Mythos being provided only through trusted access projects.
Anthropic has released the Claude Fable 5.1 and Claude Mythos 5.1, both based on the same model but configured with safety barriers of different strengths.Fable 5.1 is available on platforms such as Anthropic, AWS, Google Cloud, and Microsoft Azure. The API model name is...claude-fable-5-1Mythos 5.1 is currently only available to cybersecurity and life sciences users who have passed the Trusted Access Program audit.
Anthropic states that Fable 5.1 is expected to be approximately 25% cheaper than Fable 5 on typical workloads billed per token, with savings of up to approximately 45% on high agent loads; cache read prices are reduced to $0.25 per million tokens. These performance and cost figures are based on company testing and estimates.
refer to:Anthropic release page