The directive includes not just people located outside the U.S., but also any foreign national in the U.S., including Anthropic’s own non-citizen employees.

Given the scope of the directive, Anthropic argued it had no choice but to disable the models for all users. It clarified that access to its less powerful Claude models, including its latest Claude Opus 4.8 model, was not affected.

“We apologize for this disruption to our customers,” Anthropic wrote in a post on X. “We believe this is a misunderstanding and are working to restore access as soon as possible.”

Anthropic said in a blog post that it received the directive at 5:21 pm Eastern Time. It said the letter it received “did not provide specific details” of the government’s national security concern.

But the company also said that officials had told Anthropic that the government made the decision after learning of a technique to bypass Fable 5’s safeguards. These safeguards were designed to prevent users from accessing the powerful cybersecurity abilities of Mythos, the underlying AI model on which Fable 5 is built.

Anthropic said it believed the jailbreak the government was citing was a narrow one that would unlock Mythos’s cybersecurity capabilities in only one specific instance and not a universal one that would defeat all of Fable 5’s safeguards. It also said it believed the same jailbreak could be used to elicit similar capabilities from other publicly available models, including OpenAI’s GPT-5.5, that are not subject to similar national security export controls.

“We disagree that the finding of a narrow potential jailbreak should be cause for recalling a commercial model deployed to hundreds of millions of people,” Anthropic wrote in its blog post. “If this standard was applied across the industry, we believe it would essentially halt all new model deployments for all frontier model providers.

“As we have stated publicly, we believe the government should have the ability to block unsafe deployments, as part of a statutory process that is transparent, fair, clear, and grounded in technical facts. This action does not adhere to those principles,” Anthropic said.

AI industry insiders and policy experts reacted with disbelief to the unprecedented U.S. directive.

Some saw the move as a further attempt by the Trump administration to punish Anthropic. U.S. President Donald Trump in February ordered all federal agencies to stop using Anthropic’s models after the company refused to agree to the Pentagon’s preferred contract terms for AI vendors, which stipulated that any AI models it purchased could be used “for any lawful purpose.” Anthropic had been seeking exemptions from having its models used for autonomous weapons systems or mass domestic surveillance.

The Pentagon declared Anthropic a “supply chain risk” in early March, requiring the U.S. military to cease using its models and prohibiting defense contractors from using them for government contracts. Anthropic is challenging that designation in federal court.

Anthropic confidentially filed for a public listing earlier this month. A recent funding round valued the company at $965 billion. The government export control decision could make investors less enthusiastic about an Anthropic IPO, causing them to question whether it will be able to stay at the cutting-edge of AI model development if the government continues to single out its models for various restrictions.

Several key Trump technology policy advisors, most notably former AI and crypto czar David Sacks and Pentagon undersecretary of defense for research and engineering Emil Michael, have publicly attacked Anthropic and its executives. Sacks has accused Anthropic of being “woke” and “leftist” as well as engaging in “a sophisticated regulatory capture strategy based on fear-mongering.”

Dean Ball, an AI policy expert who briefly served in the Trump administration but is highly critical of its recent decisions around Anthropic, said on X that “I can’t tell if this is lawfare against Anthropic in particular or extreme national-security hawkery. Regardless, it is simply cartoonish.”

He added: “An administration whose posture is that we *should* export advanced AI chips to China, which also wants to ban… Britain (and every other non-American on Earth)… from using our best models? I have no words.”

But others said that Anthropic was simply reaping what it had sown. When Anthropic first debuted its Mythos model, the company argued the model was too dangerous to release broadly. When it released its Fable 5 model, which is based on Mythos, the company highlighted the safeguards it had put in place to prevent users from accessing Mythos’s full capabilities.

“If you describe your product as a munition in every press release, eventually a government takes you at your word,” Peter Girnus, a cybersecurity researcher who describes himself in his X handle as a “cyber populist,” said on X. “They wrote the legal predicate themselves and called it a brand.”

Girnus also noted that previous government efforts to limit the export of software, such as the attempt to put restrictions on powerful encryption techniques in the 1990s, have generally failed.

Gary Marcus, a frequent critic of the AI industry, said in a social media post that he thought the government’s action made little sense, especially given its oft-stated position that the U.S. must stay ahead of China in the development of powerful AI systems. The national security directive would likely convince many Chinese-born AI researchers who currently work for labs such as Anthropic and OpenAI to return to China, he said. He added it would make investors question whether American AI companies were a safe bet, given the apparently capricious nature of the Trump administration’s AI policy.

Interestingly, Ball speculated that some people concerned that AI poses existential risks to humanity, including perhaps the AI safety-minded employees at Anthropic itself, might welcome the government’s decision. This is because it might have the effect of slowing down AI development, something these AI safety proponents have been pushing for.