Microsoft has formally sided with artificial intelligence company Anthropic in a legal challenge against the Trump administration's controversial designation of Anthropic as a supply chain risk. In a federal court filing, Microsoft is challenging Defense Secretary Pete Hegseth’s decision to block Anthropic from military work, asserting that the AI company’s products pose a threat to national security. This action by the Pentagon followed an unusually public dispute stemming from Anthropic's steadfast refusal to allow unrestricted military use of its advanced AI model, Claude.

The controversy deepened when President Donald Trump publicly ordered all federal agencies to cease using Claude. Microsoft, a significant government contractor itself, argued in its Tuesday filing in San Francisco federal court that "The use of a supply chain risk designation to address a contract dispute may bring severe economic effects that are not in the public interest." The software giant further stated that the Pentagon's move "forces government contractors to comply with vague and ill-defined directions that have never before been publicly wielded against a U.S. company."

Microsoft's legal brief requests a judge to issue a temporary lifting of the designation, advocating for a more "reasoned discussion" on the matter. The Pentagon has declined to comment, citing ongoing litigation. Crucially, Microsoft also expressed support for Anthropic’s two core ethical principles that formed the crux of the stalled contract negotiations. "Microsoft also believes that American AI should not be used to conduct domestic mass surveillance or start a war without human control," the company stated, adding that this position is consistent with existing law and widely supported by American society.

Microsoft's filing is not an isolated incident of support for Anthropic. Other influential entities have also submitted briefs, including a coalition of AI developers from industry leaders like Google and OpenAI, as well as a group of organizations such as the Cato Institute and the Electronic Frontier Foundation, all backing Anthropic’s stance against the Trump administration's directive.