Anthropic blocked all customer access to Fable 5 and Mythos 5 on June 12 following a US government directive citing national security concerns. The restriction applies to foreign nationals both inside and outside the US, including Anthropic employees. Other models including Claude remain unaffected by this sudden limitation.

The company believes the government acted after learning about a jailbreaking method affecting Fable 5. Launched June 9, Fable brings Mythos' cybersecurity capabilities to the public. The model outperforms previous versions significantly, even beating Pokémon FireRed in internal tests while Claude failed at Pokémon Red.

Anthropic implemented strong safeguards to reduce cybersecurity misuse but acknowledges no model achieves perfect jailbreak resistance. Users have complained the protections are overly broad. The government provided verbal evidence of a potential narrow jailbreak from an unnamed entity.

The company disagrees that potential vulnerabilities warrant recalling a commercial model, arguing for transparent, fact-based oversight processes instead. This incident reveals escalating tensions between AI developers and government security directives.