San Francisco, California - Anthropic chief executive Dario Amodei has said there was "no choice" but to challenge in court the Pentagon's formal designation of the AI company as a risk to US national security.

The CEO, writing in a blog post on Thursday, insisted however that the practical scope of the designation ordered by Defense Secretary Pete Hegseth is narrower than initially suggested.

Amodei said the Pentagon 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 that operate within foreign adversaries, like Chinese tech company Huawei.

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In his blog post, Amodei 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 Department of Defense to use "the least restrictive means necessary."

Microsoft, one of Anthropic's biggest partners, agreed with that reading, telling US media its lawyers studied the designation and concluded that Anthropic products, including Claude, can remain available to customers other than the military/

The dispute erupted after Anthropic infuriated Hegseth by insisting its tech should not be used for mass surveillance of US citizens or fully autonomous weapons systems.

Amodei also used Thursday's statement to apologize for an internal company memo leaked to the press this week.

"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)," that memo said, referring to Greg Brockman, the president of ChatGPT-maker OpenAI, who has donated $25 million to Trump.

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Amodei called the memo an "out-of-date assessment of the current situation," written under duress on a day that saw his company under extreme pressure from the government.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