Anthropic Fables and Myths 5.1: Advanced Outreach and Research

Anthropic Fable 5.1 and Mythos 5.1 are two artificial intelligence models released on September 1, 2026. These models represent a new frontier in artificial intelligence tools for scientific work and specialized research at enterprise scale. Fable 5.1 is openly available on Anthropic platforms and public cloud providers, while Mythos 5.1 is only offered to trusted cybersecurity and life sciences partners through limited access programs. Both models address the need for advanced agents capable of executing complex projects with greater reliability, security controls, and reduced costs for specific workflows.

Key Features

• Fable 5.1: Built for ambitious coding, research, and knowledge challenges. Capable of handling entire codebases, performance tuning, code review, and supporting contexts of up to one million tokens. Provides high-quality output and can interpret charts, charts, and tables. Available for Pro, Max, Team and Enterprise plan users.

• Myth 5.1: Shares Fable’s specifications, but focuses on sensitive areas such as cybersecurity and biology. Offers reduced guarantees to qualified partners to enable cutting-edge research in these areas.

• Guarantees: Fable 5.1 includes classifiers to route labeled requests to less capable models to reduce risk. Mythos 5.1 is subject to oversight and review by Project Glasswing.

• Saving: Fable 5.1 introduces quick caching changes to reduce latency in workflows. False alarms in the security system are minimized.

Prices

• Fable 5.1 and Mythos 5.1 cost ten US dollars per million input tokens and fifty US dollars per million output tokens.

• Reading the cache for both models costs twenty-five cents per million tokens.

• Withdrawals are only available in the US at 1.1x the standard entry and exit token prices for geographic compliance.

Availability

• Mythos 5.1 is available by invitation only and is intended only for organizations in the neuroscience, life sciences, cybersecurity and related sectors. Fable 5.1 is generally available to developers and companies.

Target Audience

• Fable 5.1: Suitable for technology companies, software development teams, and product development teams working with large code bases or modular systems.

• Myth 5.1: Particularly useful for research institutions, cybersecurity firms, and regulated organizations sensitive to specific areas.

• Both models are designed for businesses that require highly skilled work, as well as startups and small businesses that need cost-effective artificial intelligence solutions.

Final Thoughts

Anthropic Fable and Mythos 5.1 models offer high-performance AI solutions tailored for demanding enterprise use. Fable 5.1 provides broad availability and performance improvements, while Mythos 5.1 serves dedicated teams working under constraints in sensitive areas. Decision makers can use Fable 5.1 for advanced capabilities and Mythos 5.1 for specialized research with fewer restrictions and the necessary verification.

Visit the official website to find out more.

Follow our stories on LinkedIn, TwitterFacebook and Instagram.