Microsoft backs Anthropic on defence in rare display of unity

Microsoft has become the first major technology company to formally back Anthropic in its legal battle against the Pentagon, urging a federal judge to block the Trump administration’s designation of the AI company as a national security risk.

After a bitter public feud about using Anthropic’s models in warfare, the Department of Defense (DoD, renamed the Department of War by the Trump administration) labelled the AI maker a “supply chain risk” last month – a classification usually reserved for foreign adversaries – which effectively bars defence contractors from using the firm’s products in Pentagon-related work.

On Tuesday, Microsoft filed a court briefing which argued that the supply chain risk label could “hamper US warfighters” by forcing contractors to strip out Anthropic’s AI tools from military systems at short notice. Microsoft integrates Anthropic’s Claude model into products it supplies directly to the US military.

Other major tech companies lent indirect support through the Chamber of Progress, a trade body funded by Google, Amazon, Apple and Nvidia, which filed a separate amicus brief arguing the designation could have a chilling effect on corporate speech.

In another filing, 37 researchers at OpenAI and Google DeepMind warned the blacklisting risked the competitiveness of the entire US AI industry.

The filings are an unusual show of tech industry solidarity, particularly given that Anthropic’s fiercest rival, OpenAI, swooped in to secure its own Pentagon dealwithin hours of Anthropic’s blacklisting. Microsoft in particular is one of the Pentagon’s most deeply embedded technology partners, holding a share of the military’s $9bn Joint Warfighting Cloud Capability contract, alongside Amazon, Google and Oracle. The tech giant also has billions of dollars worth of enterprise deals with the DoD.

“Microsoft distinguished itself from many of its big tech peers by writing an amicus brief in defence of Anthropic under their own name, as opposed to via a trade group,” says Dean Ball, former AI policy adviser to the Trump White House. “This decision deserves respect; I am happy to see Microsoft standing up for the stability of the American business environment, which is in the interest not just of all American businesses, but all Americans.”

The dispute dates back to the Pentagon’s attempts to renegotiate its AI contracts to permit “all lawful use” of Anthropic’s AI model, Claude. Anthropic’s chief executive Dario Amodei, posted a blog outlining the company’s “red lines” – the use of its models for domestic mass surveillance or fully autonomous weapons – amid pressure from Pentagon officials. Days later, President Trump branded Anthropic’s leaders as “left-wing nut jobs” and labelled the company a supply chain risk.

Microsoft has said: “The DoW needs reliable access to the country’s best technology. And everyone wants to ensure AI is not used for mass domestic surveillance or to start a war without human control. The government, the entire tech sector, and the American public need a path to achieve all these goals together.”

In November, Microsoft announced plans to invest up to $5bn in Anthropic, giving it a direct financial stake in the outcome. Kat Duffy, senior fellow at the Council on Foreign Relations, said the dispute should be concentrating minds in Europe, too: “We have never seen any US government be this aggressively interventionist with America’s leading companies.”.

“What the dispute with Anthropic has really demonstrated is an abject rejection of rule of law and due process by the DoW and through President Trump’s statements in its dealings with one of America’s leading AI companies. And, to me, that would be deeply unsettling if I were a nation looking to build on American AI.”

Photographer: Stefan Wermuth/Bloomberg via Getty Images