Microsoft Backs Anthropic in Legal Fight Against Pentagon's AI Blacklist

Microsoft has stepped into a high-profile legal battle between AI startup Anthropic and the U.S. Department of Defense, filing an amicus brief in federal court in San Francisco to support Anthropic's request for a temporary restraining order. The move comes after the Pentagon designated Anthropic as a supply-chain risk, prompting the Claude maker to sue the DOD on Monday in an effort to block what many in the tech industry are calling an unprecedented national security blacklist targeting an American AI company.

In its court filing, Microsoft argued that the Pentagon's designation should be paused while the court fully evaluates the case. The tech giant emphasized that it is directly affected by the DOD's decision, given that it integrates Anthropic's products and services into technology solutions it provides to the U.S. military. Without a temporary restraining order, Microsoft warned that contractors like itself would be forced to rapidly dismantle and rebuild existing offerings that depend on Anthropic's technology, creating significant operational and financial disruptions.

A key concern raised by Microsoft is the lack of a transition period for contractors. While the Pentagon gave itself six months to wind down its use of Anthropic, it extended no similar grace period to the companies supplying AI-powered defense solutions. Microsoft argued that a temporary pause would allow all parties time to negotiate a workable resolution, while still preserving the military's access to cutting-edge AI capabilities.

The filing also raised broader concerns about ensuring that AI technology is not deployed for domestic mass surveillance or used to initiate military conflict without meaningful human oversight. Separately, a group of 37 researchers and engineers from OpenAI and Google filed their own amicus brief on Monday in support of Anthropic, signaling growing industry-wide resistance to the Pentagon's move.