Anthropic has introduced Claude Fable 5.1 and Claude Mythos 5.1, new artificial intelligence models designed to improve performance on coding and complex knowledge-work tasks while making advanced AI capabilities more practical to deploy.

The models were announced by Anthropic and reported by Cointelegraph. Claude Fable 5.1 is positioned as the company’s most capable generally available model, while Mythos 5.1 is being offered on a limited, invitation-only basis to vetted organizations through Anthropic’s trusted access programs.

Stronger Coding and Long-Running Workflows

Anthropic said Fable 5.1 is designed for demanding coding projects, long-running agentic tasks, and complex research and analysis. The model can work across large codebases, conduct code reviews, use tools, and handle multi-stage assignments with less continuous supervision.

The model has a 1 million-token context window and a maximum output of 128,000 tokens. Anthropic lists API pricing at $10 per million input tokens and $50 per million output tokens, while cached reads are priced at $0.25 per million tokens.

Anthropic’s pricing structure also reflects the growing importance of controlling inference costs as businesses move from conventional chatbot interactions toward AI agents capable of completing extended workflows. For developers and enterprises, the longer context window and higher output cap are especially relevant in settings where models need to keep track of large repositories, documentation, or research threads without losing continuity.

Mythos 5.1 Remains Restricted

Claude Mythos 5.1 shares the same underlying capabilities as Fable 5.1 but is subject to a more restricted deployment model because of its capabilities in areas such as cybersecurity and biology.

Anthropic said access remains limited to vetted organizations, with additional safeguards intended to reduce the potential for misuse. Fable 5.1 incorporates similar protections, including restrictions around penetration testing, exploit generation, and certain biology-related requests.

The distinction highlights a broader challenge for AI developers: improving model capabilities while maintaining controls over applications where increasingly autonomous systems could create significant security or safety risks. It also shows how access policies can become part of product design, not just a deployment afterthought, as model makers balance wider availability with tighter review for sensitive use cases.

Next Test for Anthropic’s New Models

Fable 5.1 is now generally available across Anthropic’s ecosystem and several major cloud platforms, while Mythos 5.1 remains restricted to approved users.

The next key question will be how developers and enterprises adopt the models in real-world coding and knowledge-work environments, particularly whether their additional capabilities can translate into measurable productivity gains while keeping deployment costs and safety risks under control. In practice, that will likely be judged by how well the models handle repeated, multi-step work where reliability, oversight, and token efficiency matter as much as raw capability.

writer: Ethan Collins

Crypto Journalist

Ethan Collins reports on developments across the cryptocurrency and blockchain sector. His work covers market movements, protocol updates, regulatory changes, and emerging trends in digital assets. He focuses on presenting complex topics in a clear and accessible manner for a broad readership.