Fable

Fable (officially Claude Fable 5) is a large language model developed by Anthropic, positioned within the company's highest capability tier, which Anthropic designates the "Mythos class" — its most powerful AI systems to date. The model is designed for complex reasoning, generation, and analysis tasks at a frontier level and represents a significant step in Anthropic's public model lineup.

The release drew attention well beyond the AI research community, with technology investors viewing Fable's launch as a signal for sustained demand in AI infrastructure and semiconductor markets. The launch was also accompanied by controversy: reports emerged around claims of guardrail bypass vulnerabilities and allegations of throttled researcher access, highlighting the persistent tension between rapid capability deployment and rigorous safety assurance.

Fable 5 subsequently became a focal point of U.S. government policy, with the Trump administration imposing export controls that block foreign nationals from accessing both Fable 5 and the related Mythos model. Cybersecurity experts criticized the restrictions as potentially counterproductive, and the episode marked a notable escalation in federal oversight of frontier AI model distribution, raising broader questions about how governments will regulate access to advanced AI systems going forward.