Microsoft submitted a formal brief in San Francisco federal court backing Anthropic’s appeal to pause the Department of Defense’s classification of the startup as a supply chain risk. The company emphasized that a temporary restraining order is needed to prevent immediate operational disruptions while the court examines the case.

The filing states that forcing government contractors to remove Anthropic’s AI tools without transition would create costly redesigns of existing systems. Microsoft highlighted its integration of Anthropic technology in current defense applications, warning of potential delays and budget overruns if access is suddenly cut off.

Anthropic filed suit seeking to block the Pentagon’s six-month phase-out of its AI software, arguing that no transition period was provided for current contractors. Microsoft’s brief aims to strengthen this challenge by underscoring shared reliance on Anthropic for advanced AI capabilities in defense missions.

The court will consider whether to grant the temporary restraining order, which would pause the blacklist designation during further proceedings. If approved, stakeholders would gain time to negotiate revised terms or identify alternative solutions without immediate compliance pressures.