The company said it received ⁠an export control directive to suspend access to Fable 5 and Mythos 5 for foreign nationals.

The AI firm Anthropic has blocked access to its newly released cutting-edge software, following an order by the United States government.

In a blog post published Friday, the company behind the Claude chatbot said government agencies had instructed it to prevent all foreign nationals from accessing the AI models Fable 5 and Mythos 5, citing national security concerns.

Anthropic said it received the order at 5:21pm (21:21 GMT) on Friday and that the letter did not explain the government’s specific security concern in detail.

The ban also affects foreigners currently in the US – including those working at Anthropic.

As a result of the order, the company had to cut off access for everyone at short notice, it said.

The artificial intelligence behind Anthropic’s Mythos AI model is particularly adept at detecting software vulnerabilities, some of which have remained undiscovered for decades.

This capability has been used by US authorities and selected companies to plug security gaps.

However, a concern from the outset has been that such AI could become a dangerous cyberweapon in the wrong hands.

The Fable 5 model, released just this week, is based on Mythos technology, but its cybersecurity and biotechnology capabilities are blocked.

Mythos 5 is the non-public full version, which should continue to be used only by government agencies and selected corporate partners to harden their systems.

Anthropic emphasised that it had so far received only partial information from the government.

The company said it had reviewed a report which, in its assessment, was likely to have triggered the order.

Anthropic’s experts concluded that this referred to a limited capability to use the AI to review specific programme code and correct errors.

Models from other providers, such as GPT-5.5 from rival OpenAI, also possess this capability, the company stressed.

Anthropic said it disagreed that software used by hundreds of millions of users should be blocked for this reason, and that the safety measures in Fable 5 have been extensively tested.

Earlier this month, Anthropic proposed that the world’s top artificial intelligence companies coordinate to pause development of advanced AI systems, warning that the technology is improving so quickly that there is a risk humans would lose control.

The company said in a blog post in early June that, as cutting-edge AI gets increasingly faster at carrying out tasks, “it would be good for the world to have the option to slow or temporarily pause” its development.