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Microsoft Breaks Silicon Valley Silence, Backs Anthropic in Pentagon Legal Fight
In a significant departure from the tech industry’s recent caution, Microsoft has publicly sided with AI startup Anthropic in its legal battle against the U.S. Department of Defense. The software giant filed an amicus curiae brief on Tuesday urging a federal court to block the Pentagon’s decision to designate Anthropic as a “supply chain risk,” calling the move “drastic” and “unprecedented.” Microsoft argues the designation threatens broad, negative ramifications for the entire U.S. technology sector and national security.
A Rare and Strategic Intervention
Microsoft’s filing, submitted in courts in California and the District of Columbia, marks the first time a major Big Tech company has openly challenged the Trump administration’s actions against a U.S.-based AI firm. The company is not a defendant in the case but is seeking a temporary restraining order to halt enforcement of the Pentagon’s decision while Anthropic’s lawsuit proceeds. According to the brief, Microsoft believes a pause would allow for “reasoned discussion” and a negotiated settlement regarding the appropriate use of AI in military and intelligence operations.
This intervention highlights a deep rift within Silicon Valley. Since President Trump’s return to office, much of the tech industry has avoided direct confrontation with the administration. Microsoft’s stance, however, is rooted in its own extensive government contracting business and its strategic, multi-billion-dollar partnership with Anthropic. The two companies signed a $30 billion cloud-computing deal in November 2023, and Microsoft is currently integrating Anthropic’s Claude coding models into its widely-used business software suite, which serves numerous federal agencies.
The Collapse of Negotiations and the “Red Lines”
The conflict stems from negotiations that broke down in late April. Anthropic, a company valued at approximately $18 billion following recent funding rounds, rejected a Pentagon contract for the military deployment of its technology. CEO Dario Amodei insisted on establishing firm ethical “red lines,” prohibiting the use of its AI models for lethal autonomous weapons systems and for the mass surveillance of U.S. citizens.
In response, Defense Secretary Pete Hegseth moved to cut Anthropic from the Pentagon’s supply chain—a regulatory action typically reserved for companies based in adversarial nations like China or Russia. The administration has also directed all federal agencies to cease using the Claude chatbot, framing it
