Anthropic Launches Claude Fable 5.1 and Restricted Mythos 5.1 for Advanced Coding, Cybersecurity and Scientific Research Anthropic has launched Claude Fable 5.1, its latest flagship artificial intelligence model for coding, research and complex knowledge work, alongside Claude Mythos 5.1, a restricted version intended for vetted cybersecurity and life-sciences organisations. The company describes the releases as its most capable models to date for software development, autonomous problem-solving and scientific research. Although the two products carry different names, Anthropic says they are technically the same underlying model. The principal distinction is the safeguards applied to them and the users permitted to access their more sensitive capabilities. Fable 5.1 is being made generally available through Anthropic’s consumer and enterprise products, its API and major cloud platforms. Mythos 5.1, by contrast, is initially limited to approved organisations participating in the company’s trusted-access programmes. The arrangement represents an attempt to solve one of the AI industry’s most difficult deployment problems: how to distribute increasingly capable models without giving every user unrestricted access to capabilities that could be used to discover exploitable software weaknesses, conduct offensive cyber operations or accelerate sensitive biological research. Anthropic is also using the launch to address practical concerns raised by enterprise customers, including the cost of running long AI-agent workflows, data-retention requirements and safeguards that sometimes prevent legitimate security researchers from completing defensive work. One model, two levels of access Claude Fable 5.1 and Claude Mythos 5.1 are not separate models trained for different purposes. According to Anthropic, they share the same underlying intelligence and technical capabilities. Fable 5.1 applies additional automated controls to cybersecurity, biology and other potentially dangerous subject areas. Mythos 5.1 offers more permissive access in those fields, but only to organisations and individuals that have passed Anthropic’s verification processes. The distinction is particularly important in cybersecurity. Highly