The U.S. government ordered Anthropic to block all access to its Fable 5 and Mythos 5 AI models for foreign nationals citing national security concerns, forcing the company to cut off the models entirely for all customers.

What happened: On Friday evening, the government directed Anthropic to block access to Fable 5 and Mythos 5 for all foreign nationals both inside and outside the U.S., as well as company employees. To comply, Anthropic has completely cut off access to both models for all customers.

Why it matters: The government did not provide specific details of its national security concern, and Anthropic states that evidence of potential vulnerabilities was provided only verbally. Anthropic contends that the vulnerabilities discovered were minor and available via other models, including GPT 5.5, raising questions about the basis for the broad access restriction.

What to watch: Anthropic has documented its earlier safeguarding steps, including work with the U.S. and UK governments and changes to its data retention policy. The company has stated it has not received disclosure of a concerning non-universal potential jailbreak that led to a harmful result.