Fable 5 and Mythos 5 share the same underlying model. Fable 5 is AnthropicAn AI safety company — creators of the Claude family of language models.'s top generally available tier: safety classifiers route sensitive cybersecurity and biology queries to Claude Opus 4.8 instead. Mythos 5 lifts those safeguards for vetted partners in Project Glasswing — AnthropicAn AI safety company — creators of the Claude family of language models.'s answer to releasing a model strong enough to help defenders without open-sourcing misuse risk. Both ship at $10/$50 per million tokens.

AnthropicAn AI safety company — creators of the Claude family of language models. split one frontier model into public Fable and restricted Mythos to balance capability and safety.

It defined how labs ship models with dangerous dual-use skills without a single open release.