On June 9, 2026, Anthropic announced the release of Claude Fable 5 and Claude Mythos 5, marking a new chapter in frontier AI. Fable 5 is the first Mythos-class model available to the public, but with carefully designed safety classifiers that block responses to queries about cybersecurity and biochemistry threats. Meanwhile, Mythos 5 is an unrestricted version offered exclusively to vetted cybersecurity professionals through Project Glasswing. This dual-release strategy aims to balance the immense power of advanced AI with responsible deployment.
Stripe’s Migration Milestone
In a demonstration of Fable 5’s coding prowess, Stripe migrated its massive 50-million-line Ruby codebase in a single day using the model. This feat showcases how frontier AI can handle real-world engineering challenges at scale.
Benchmark Dominance
Fable 5 outperforms GPT-5.5 on physics benchmarks, demonstrating superior reasoning in scientific domains. It also achieved novel drug design results, signaling potential breakthroughs in pharmaceuticals.
Gaming Capabilities
Remarkably, Fable 5 beat Pokémon FireRed using only vision input, no human-like controls, proving its ability to navigate complex game environments autonomously.
Pricing and Reliability
Anthropic set pricing at $10 per million input tokens and $50 per million output tokens for Fable 5. The model requires no fallback in over 95% of sessions, indicating high reliability for production use.
Mythos 5 and Safety
Mythos 5, available under Project Glasswing, provides unrestricted capabilities for cybersecurity defense. This allows ethical hackers and security teams to leverage the full power of a Mythos-class model to analyze threats and develop defenses, while keeping the most dangerous capabilities out of the hands of malicious actors.
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