The company received the export control directive to suspend access to Fable 5 and Mythos 5 for all foreign nationals, without being given specific details of its national security concern, Anthropic said in a statement.
It is Anthropic's understanding the government believes there is a method of bypassing, or "jailbreaking," a safeguard that would prevent Fable 5 from being used in identifying software vulnerabilities, the company said.
The order comes just as a previous dispute between Trump administration officials and IPO-bound Anthropic showed signs of easing across parts of the US government.
Anthropic's relationship with the government ruptured this year after it refused to allow the US military to use its AI models for domestic surveillance and fully autonomous weapons systems. The government responded by putting Anthropic on a supply chain blacklist, set to take effect later in the year.
The action also marks a major escalation of US efforts to halt foreign adversaries' AI capabilities. For years, US export controls have focused on the chips and tools that power AI rather than on restricting foreign access to AI itself.
Anthropic said the government has given it only "verbal evidence of a potential narrow, non-universal jailbreak".
"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," the company said.
The Pentagon's chief information officer, Kirsten Davies, said in a post on X that the Defence Department supported prioritising national security.
"Some things are simply more important than revenue cycles, clickbait, and pre-IPO valuation. America First. Always," Davies said.
Anthropic confidentially filed for a US IPO last month, edging ahead of rival OpenAI in the race to reach public markets.
Earlier this week, Anthropic rolled out an AI model named Claude Fable 5, representing a new tier of capability it calls "Mythos-class." The model is accompanied by guardrails barring its use in risky areas such as cybersecurity, which some users have complained are "overly broad," Anthropic said.
Experts say Mythos models, in the wrong hands, could dramatically accelerate sophisticated cyberattacks, particularly in sectors such as banking that rely on complex, interconnected, and often decades-old technology systems.
Anthropic said it had worked with the US government, among others, on safety ahead of the Fable launch and that models from rival AI providers showed a similar ability to unearth minor bugs in code.
"The net effect of this order is that we must abruptly disable Fable 5 and Mythos 5 for all our customers to ensure compliance. Access to all other Anthropic models will not be affected," Anthropic said.
Anthropic said it believed there was a "misunderstanding" and it is working to restore access to the models as soon as possible.
"If this standard was applied across the industry, we believe it would essentially halt all new model deployments for all frontier model providers," the company said.
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