Claude 5 Fable is the first publicly released model in the Mythos class. It demonstrates significant advancements over previous AI models, although its guardrails restrict its use in cybersecurity applications.

Anthropic's Mythos project utilized a budget of under $20,000 for a comprehensive search process involving approximately a thousand scaffolded runs and several dozen findings. The initial impression of Mythos being able to find a devastating bug for that price is misleading, as the findings were part of a larger testing effort.