Microsoft has become the most prominent champion of Anthropic’s cause as the AI company’s dual lawsuits against the Pentagon gain momentum in federal court, filing an amicus brief in San Francisco that calls for a temporary restraining order against the Defense Department’s unprecedented supply-chain risk designation. The brief argued that the designation threatens the defense and commercial technology supply chains that have come to depend on Anthropic’s AI. Amazon, Google, Apple, and OpenAI have also filed supporting briefs, propelling Anthropic’s legal challenge to the forefront of national attention.
The legal battle traces back to a $200 million contract that would have deployed Anthropic’s Claude AI on classified military systems. Anthropic insisted on protections preventing use of its technology for mass surveillance or autonomous lethal weapons, conditions the Pentagon refused. Defense Secretary Pete Hegseth labeled the company a supply-chain risk, triggering the cancellation of its government contracts.
Microsoft’s championship of Anthropic is anchored in its direct use of Anthropic’s technology in federal military systems and its partnership in the Pentagon’s $9 billion cloud computing contract. Additional federal agreements spanning defense, intelligence, and civilian agencies further deepen the company’s stake in this dispute. Microsoft publicly argued that responsible AI governance and national security required partnership between government and industry, not confrontation.
Anthropic’s court filings argued that the supply-chain risk designation was an unconstitutional act of retaliation for publicly advocating responsible AI development, violating First Amendment rights. The company disclosed that it does not currently believe Claude is safe or reliable enough for lethal autonomous operations. The Pentagon’s technology chief publicly ruled out any possibility of renegotiation, hardening the confrontation.
Congressional Democrats are simultaneously pressing the Pentagon for answers about whether AI was involved in a strike in Iran that reportedly killed over 175 civilians at a school. Their inquiries focus on AI targeting tools and human oversight. The growing momentum of Anthropic’s lawsuits, bolstered by Microsoft’s championship and the industry coalition, is creating a legal and political force that the Pentagon will be hard-pressed to resist.