Microsoft Doubles Down on Support for Anthropic as Pentagon Stands Firm on Unprecedented AI Blacklist

As the Pentagon stands firm on its unprecedented decision to blacklist Anthropic, Microsoft has doubled down on its support for the AI company by filing an amicus brief in a San Francisco federal court that calls for a temporary restraining order against the supply-chain risk designation. The brief argued that the designation, if allowed to stand, would cause immediate and serious harm to the defense and commercial technology supply chains. Amazon, Google, Apple, and OpenAI have also filed in support of Anthropic, creating a formidable industry coalition against the government’s position.
The Pentagon’s firm stance follows the breakdown of a $200 million contract negotiation in which Anthropic refused to allow its Claude AI to be used for mass surveillance of US citizens or to power autonomous lethal weapons. Defense Secretary Pete Hegseth formalized the supply-chain risk designation, triggering the cancellation of Anthropic’s government contracts. The Pentagon’s technology chief publicly ruled out any prospect of renegotiation.
Microsoft’s doubling down on support for Anthropic is grounded in its direct use of Anthropic’s technology in federal military systems and its participation in the Pentagon’s $9 billion cloud computing contract. The company also holds additional federal agreements spanning defense, intelligence, and civilian agencies. Microsoft publicly argued that responsible AI governance and effective national defense were goals that the government and industry needed to pursue together.
Anthropic filed two simultaneous lawsuits in California and Washington DC challenging the designation as unconstitutional and unprecedented. The company’s court filings argued that the supply-chain risk label was being misused as a political weapon against a US company for its publicly held AI safety positions. Anthropic disclosed that it does not currently believe Claude is safe or reliable enough for lethal autonomous operations.
Congressional Democrats have separately pressed the Pentagon for answers about whether AI was involved in a strike in Iran that reportedly killed over 175 civilians at a school, raising concerns about AI targeting tools and human oversight. These inquiries are adding political pressure to an already intense legal confrontation. Together, Microsoft’s doubled-down support, the industry coalition, and congressional scrutiny are creating a powerful challenge to the Pentagon’s firm stance on the Anthropic blacklist.