Anthropic gains Microsoft’s backing in Pentagon Court battle

Microsoft filed on Tuesday a brief in support of Anthropic’s lawsuit asking the court to temporarily block the US Department of Defense’s designation of the AI startup as a supply-chain risk.

In an amicus brief filing in a federal court in San Francisco, Microsoft backed Anthropic’s request for a temporary restraining order against the Pentagon order, arguing that its determination should be paused while the court considers the case.

Microsoft, which integrates the AI lab’s products and services into technology it provides to the US military, said that it was directly impacted by the DOD designation.

The Claude maker had filed a lawsuit to block the Pentagon from placing it on a national security blacklist on Monday, escalating a high-stakes battle with the US military over usage restrictions on its technology.

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Microsoft’s filing argued the TRO is needed to prevent costly disruptions for suppliers, who would otherwise have to rapidly rebuild offerings that rely on Anthropic’s products. The judge overseeing the case must approve Microsoft’s request to file the brief before it is officially entered, but courts often permit outside parties to weigh in on important cases.

While the Pentagon gave itself six months to phase out Anthropic, it did not provide the same transition period for contractors that use Anthropic’s products or services to perform under DOD, Microsoft said.

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“Should this action proceed without the entry of a temporary restraining order, Microsoft and other government contractors with expertise in developing solutions to support US government missions will be forced to account for a new risk in their business planning,” the company said.

Microsoft added that a temporary restraining order would allow time to negotiate a solution while protecting military access to advanced technology and ensuring AI is not used for domestic mass surveillance or to start a war without human control.

On Monday, a group of 37 researchers and engineers from OpenAI and Google had also filed an amicus brief in support of Anthropic.