The CEO, writing in a blog post on Thursday, insisted however that the ruling's practical scope is narrower than initially suggested, signaling that the designation would not have a catastrophic effect on the company.

Amodei said the Department of War -- the name preferred by the Trump administration for the Department of Defense -- confirmed in a letter that Anthropic and its products, including its widely-used Claude AI model, have been deemed a supply chain risk.

It is the first time a US company has ever been publicly given such a designation, a label typically reserved for organizations from foreign adversary countries, like Chinese tech company Huawei.

Amodei, in his blog post, said the company disputes the legal basis of the action but sought to reassure customers.

"It plainly applies only to the use of Claude by customers as a direct part of contracts with the Department of War, not all use of Claude by customers who have such contracts," he wrote.

The designation will require defense vendors and contractors to certify that they don't use Anthropic's models in their work with the Pentagon.

But Amodei argued that under the relevant statute, the intention is "to protect the government rather than to punish a supplier" and requires the Pentagon to use "the least restrictive means necessary."

Microsoft, one of Anthropic's biggest partners, agreed with that reading, concluding that Anthropic products can remain available to its customers other than the Department of War.

Google and Amazon Web Services (AWS), the other major cloud giants on which Anthropic's Claude is often delivered to businesses customers, also said they were standing by the company's products except for US military use.

- 'Sloppy' -

The dispute erupted after Anthropic infuriated Pentagon chief Pete Hegseth by insisting its technology should not be used for mass surveillance or fully autonomous weapons systems.

Washington hit back, saying the Pentagon operates within the law and that contracted suppliers cannot dictate terms on how their products are used.

Amodei also used the statement to apologize for an internal company memo leaked to the press this week, in which he told staff the actions against the company were politically motivated.

"The real reasons" the Trump administration "do not like us is that we haven't donated to Trump (while OpenAI/Greg have donated a lot)," Amodei said, referring to Greg Brockman, the president of ChatGPT-maker OpenAI, who has donated $25 million to Trump.

Amodei called the memo an "out-of-date assessment of the current situation," written under duress on a day that saw his company under extreme pressure from the government.

OpenAI initially swooped in to replace Anthropic in its contract with the US military, but that move backfired when senior OpenAI staff expressed discomfort with the deal.

OpenAI CEO Sam Altman later said the deal was "sloppy" and that he was working to revise it.

The standoff with the Pentagon has had some silver lining for Anthropic, which was founded in 2021 by former staffers of OpenAI, with a focus on AI safety.

The conflict has helped propel the Claude app to the top of download rankings on Apple and Google smartphones.

Anthropic also indicated to AFP that the number of paying users of its Claude model had doubled since the beginning of the year and that its app is currently downloaded more than a million times a day.