Washington gave the AI startup until Friday afternoon to agree to unconditional military use of its technology - even where that clashes with the company's own ethical standards.

At the heart of the dispute is Anthropic's refusal to allow its Claude models to be used for the mass surveillance of US citizens or deployed in fully autonomous weapons systems.

The conflict has drawn a show of solidarity from the industry.

An open letter titled "We Will Not Be Divided," signed as of Friday by 336 Google DeepMind staffers and 68 from OpenAI, called on tech leaders to hold the line together.

"We hope our leaders will put aside their differences and stand together to continue to refuse the Department of War's current demands for permission to use our models for domestic mass surveillance and autonomously killing people without human oversight," the letter said.

"They're trying to divide each company with fear that the other will give in. That strategy only works if none of us know where the others stand," it added.

OpenAI CEO Sam Altman told employees on Thursday that he too was seeking an agreement with the Pentagon that would include red lines similar to Anthropic's, and that he hoped to help broker a resolution, the Wall Street Journal first reported.

"We have long believed that AI should not be used for mass surveillance or autonomous lethal weapons, and that humans should remain in the loop for high-stakes automated decisions," he wrote.

The Department of Defense, for its part, has pushed back on Anthropic's position, insisting it always operates within the law and that contracted suppliers cannot set their own terms on how their products are used by the military.

The Pentagon's ultimatum requires Anthropic to agree to unrestricted military use of its technology by 5:01 pm (22:01 GMT) Friday or face compulsion under the Defense Production Act. The Cold War-era law, last invoked during the Covid pandemic, grants the federal government sweeping powers to direct private industry toward national security priorities.

The Pentagon has also threatened to designate Anthropic a supply chain risk -- a label typically reserved for companies from adversary nations - which could severely damage its ability to work with the US government and harm its broader reputation.

Industry representatives in Washington are pressing hard for a negotiated outcome, warning that the confrontation risks damaging the AI sector as a whole.

"Decisions about military AI cannot be settled through ad hoc standoffs between the Pentagon and individual firms," said Daniel Castro, vice president of the Information Technology and Innovation Foundation.

"If certain AI capabilities are deemed essential for national defense, those expectations should be debated openly and written into law."