Microsoft has backed Anthropic with the full force of its legal and corporate resources by filing an amicus brief in a San Francisco federal court that challenges the Pentagon’s supply-chain risk designation in the strongest possible terms. The brief called for a temporary restraining order and argued that the designation threatens the foundational technology networks supporting national defense. Amazon, Google, Apple, and OpenAI have also filed in support of Anthropic, making this a historic legal challenge to a government action by the technology industry.
The Pentagon’s designation followed the breakdown of a $200 million contract negotiation in which Anthropic refused to allow its AI to be used for mass surveillance or autonomous lethal weapons. Defense Secretary Pete Hegseth applied the supply-chain risk label, triggering the cancellation of Anthropic’s government contracts. Anthropic filed two simultaneous lawsuits in California and Washington DC, challenging the designation as unconstitutional and unprecedented for a US company.
Microsoft’s full backing is grounded in its direct use of Anthropic’s AI in federal military systems and its partnership in the Pentagon’s $9 billion cloud computing contract. The company also holds additional agreements with defense, intelligence, and civilian agencies. Microsoft publicly argued that the government and technology sector must work together to ensure advanced AI serves national security without crossing ethical lines.
Anthropic’s lawsuits argued that the supply-chain risk designation was an unconstitutional act of ideological retaliation for the company’s public advocacy of responsible AI development. The company disclosed that it does not currently believe Claude is safe or reliable enough for lethal autonomous operations, which it said was the genuine basis for its contract demands. The Pentagon’s technology chief publicly ruled out any possibility of renewed negotiations.
Congressional Democrats have separately written to the Pentagon demanding information about whether AI was used in a strike in Iran that reportedly killed over 175 civilians at a school. Their inquiries are adding legislative urgency to an already intense legal confrontation. The combination of Microsoft’s full backing, the industry coalition, and congressional pressure is creating a historic challenge to the Pentagon’s AI governance approach that could reshape national security policy for years to come.
