Claude Fable 5: The New Frontier of Mythos-Class AI Capabilities

Experience the Next Evolution of Intelligence: Introducing Claude Fable 5

The landscape of artificial intelligence has just shifted. We are thrilled to announce the launch of Claude Fable 5, a powerhouse Mythos-class model designed to push the boundaries of what AI can achieve while maintaining a rigorous commitment to safety. From complex software architecture to groundbreaking scientific discovery, Fable 5 isn’t just an update—it’s a leap forward in general AI capability.

Whether you are a developer, a researcher, or a business leader, Claude Fable 5 delivers state-of-the-art performance across nearly every tested benchmark, proving that the more complex the task, the greater Fable 5’s advantage over previous generations.

Unrivalled Performance Across Key Domains

Claude Fable 5 excels where other models struggle, offering deep reasoning and autonomous execution in several critical areas:

• Revolutionary Software Engineering: Fable 5 is transforming the development lifecycle. In real-world testing with Stripe, the model compressed months of engineering work into mere days, completing a massive codebase migration in a 50-million-line Ruby environment that would have typically required a full team two months to execute manually.
• Advanced Knowledge Work: For high-level analytical tasks, Fable 5 is currently the gold standard. It has achieved top scores in senior-level financial reasoning, excelling in document interpretation, root-cause analysis, and complex problem-solving.
• Next-Gen Computer Vision: Beyond simple image recognition, Fable 5 can rebuild a web application’s source code from screenshots alone and extract precise data from intricate scientific figures.
• Enhanced Memory and Context: With the ability to stay focused across millions of tokens, Fable 5 utilizes persistent file-based memory to improve its outputs, showing a massive performance boost in complex, long-running simulations and games.

Claude Mythos 5: Empowering Science and Security

Alongside the general release, we are introducing Claude Mythos 5. While it shares the same core architecture as Fable 5, Mythos 5 is a specialized version with lifted safeguards in specific areas, reserved for a trusted group of cyber-defenders and scientific researchers via advanced research frameworks.

The impact of Mythos 5 is already being felt in the life sciences:

• Drug Design: Internal experts reported a 10x acceleration in the protein design process, with the AI matching or exceeding skilled human operators in selecting binding sites and running bioinformatics tools.
• Genomics & Molecular Biology: Mythos 5 has autonomously conducted genomics research across 138 species, designing a custom ML model that outperformed existing research published in leading journals.

A Balanced Approach to AI Safety

With great power comes great responsibility. To prevent the misuse of these capabilities—particularly in cybersecurity and biology—we have implemented a sophisticated system of AI classifiers. These safeguards detect potential misuse or “jailbreak” attempts in real-time.

If a query is flagged as potentially harmful, the system seamlessly falls back to Claude Opus 4.8. This ensures that users still receive a highly capable response without compromising global security. Our data shows that over 95% of sessions proceed without any fallback, meaning the vast majority of users experience the full power of Fable 5 uninterrupted.

Pricing and Availability

We believe advanced AI should be accessible. Claude Fable 5 is available now via the Claude API with a highly competitive pricing structure:

• Input Tokens: $10 per million
• Output Tokens: $50 per million

This represents a significant cost reduction (less than half the price of Claude Mythos Preview), making frontier-level AI viable for startups and enterprises alike. Developers can start integrating claude-fable-5 into their workflows today through the official API.

Stay tuned as we continue to refine our safeguards and expand the Trusted Access Program for biomedical and cybersecurity pioneers.