In what is shaping up to be a defining legal confrontation over the use of artificial intelligence in national security, Microsoft has entered the fray by filing a supporting court brief on behalf of Anthropic in its suit against the Pentagon. The filing, submitted to a federal court in San Francisco, argued that the Defense Department’s supply-chain risk designation against Anthropic could severely disrupt critical technology supply chains. The brief is backed by a parallel filing from Google, Amazon, Apple, and OpenAI, creating an unprecedented alignment of tech industry power behind a single legal cause.
The controversy erupted after Anthropic refused to agree to Pentagon demands that its AI be deployed without restrictions on mass surveillance or autonomous lethal weapons as part of a $200 million contract. Defense Secretary Pete Hegseth responded to the breakdown of talks by applying the supply-chain risk designation, a label that had never before been used against a US company. Anthropic’s existing government contracts began to be cancelled shortly after the designation was formalized.
Microsoft’s filing is informed by its own deep integration of Anthropic’s AI into military systems and its status as a core partner in the Pentagon’s $9 billion cloud computing contract. The company also holds additional agreements with federal agencies spanning defense, intelligence, and civilian services. Microsoft’s public statement called for a path forward that ensures the military’s access to the best AI tools while preventing those tools from being used for domestic surveillance or unauthorized lethal action.
Anthropic’s dual lawsuits, filed in both California and Washington DC, argue that the supply-chain risk designation was applied not for legitimate security reasons but as retaliation for the company’s public AI safety positions. The company’s court documents disclosed that it does not currently have confidence in Claude’s safety and reliability in lethal autonomous warfare scenarios. The Pentagon’s chief technology officer publicly ended any hope of renegotiation, declaring unambiguously that the agency would not return to the table.
The legal battle is unfolding as Congress investigates whether AI played a role in a US military strike in Iran that reportedly resulted in the deaths of more than 175 civilians at an elementary school. House Democrats have formally asked the Pentagon whether AI targeting systems were used and what human review processes were in place. These inquiries, combined with Anthropic’s lawsuits and the industry’s unified response, have created a moment of reckoning for US policy on AI in warfare.