Claude Mythos 5 vs. Claude Fable 5.1

Claude Mythos 5 is Anthropic’s restricted-access Mythos-class AI model built for trusted organizations that require the highest level of Claude capability. The model shares the same underlying architecture as Claude Fable 5, but is offered with certain safeguards removed for approved use cases and vetted users. Claude Mythos 5 is designed for advanced cybersecurity, software engineering, scientific discovery, long-context reasoning, and autonomous research workflows. It is initially deployed through Project Glasswing for cyberdefenders and critical infrastructure providers. The model is intended to help security teams analyze complex systems, support defensive cybersecurity work, and protect important software environments. Claude Mythos 5 also demonstrates major potential in life sciences, where it can assist with protein design, binding-site selection, bioinformatics workflows, and research hypothesis generation. Anthropic reports that the model can carry out extended technical tasks, recover from failures, and operate with a high degree of autonomy. Its capabilities in genomics include assembling large-scale single-cell datasets and designing custom machine learning approaches for biological research. Because these capabilities may be dual-use, Anthropic limits access through trusted programs and applies a 30-day retention policy for Mythos-class traffic. The model is priced at $10 per million input tokens and $50 per million output tokens. Claude Mythos 5 helps vetted organizations apply frontier AI to critical defense, infrastructure, and scientific problems while maintaining controlled access and oversight.

Claude Fable 5.1 is an advanced general-purpose AI model from Anthropic focused on coding, scientific research, knowledge work, business processes, and long-horizon agentic reasoning. It is the generally available counterpart to Claude Mythos 5.1, which uses the same underlying model but is offered with different safeguards for vetted cybersecurity and life sciences users. Compared with Claude Fable 5, Fable 5.1 shows stronger performance across agentic coding, research, computer use, multidisciplinary reasoning, business workflow automation, and other complex benchmarks. The model is designed to remain effective during long-running tasks that involve planning, tool use, repeated verification, code modification, research, and multi-step decision making. In software engineering scenarios, it can investigate difficult bugs, trace problems across large codebases, perform code review, and work through complex implementation tasks with less supervision. Anthropic also positions Fable 5.1 as a stronger research model, with demonstrated capabilities in scientific analysis, computational modeling, and other technically demanding workflows. Improvements to cache-read pricing reduce the cost of reusing previously processed context, making the model more economical for workflows that involve long conversations, large codebases, or repeated tool calls. Fable 5.1 introduces updated enterprise privacy and security options, including Enterprise Frontier Safeguards and zero-data-retention access for eligible customers during the rollout period. Its cybersecurity protections are designed to permit more benign defensive security work, including vulnerability discovery, while continuing to restrict higher-risk activities such as exploit development and certain penetration-testing tasks. The model is available through Claude.ai, Claude Code, Claude Cowork, the Claude API, Amazon Web Services, Google Cloud, and Microsoft Azure under the claude-fable-5-1 model identifier for API users.