Anthropic on Tuesday announced the general availability of Claude Fable 5, a powerful Mythos-class AI model engineered with new safeguards that specifically restrict its use in high-risk domains, including cybersecurity.
The AI giant says this marks the first time a model of this capability class has been deemed safe enough for widespread public and developer access.
While Fable 5 demonstrates good performance — surpassing prior models in software engineering, knowledge work, vision, and long-running tasks — the company prioritized safety by implementing targeted blocks.
In sensitive areas such as cybersecurity and biology, the model automatically falls back to the less capable Claude Opus 4.8 to prevent potential misuse. Early usage data indicates that at least 95% of sessions run entirely on Fable 5’s capabilities without triggering any fallback.
“The uplift from Mythos-level capabilities is valuable to many adversaries — for instance, those who could financially gain from cyberattacks — and we therefore expect them to be motivated to try to circumvent our safety measures,” Anthropic noted.
