Microsoft CEO Satya Nadella attends the 56th annual World Economic Forum (WEF) meeting in Davos, Switzerland, January 20, 2026.
Denis Balibouse | Reuters
Microsoft threw its support behind Anthropic on Tuesday, saying a judge should issue a restraining order that would block the Pentagon’s designation of the artificial intelligence giant as a supply chain risk “for all existing contracts.”
Such an order would “enable a more orderly transition and avoid disrupting the American military’s ongoing use of advanced AI,” Microsoft said in a filing in U.S. District Court in San Francisco. Without that order, Microsoft warned that it, along with other technology companies, would need to “act immediately to alter existing product and contract configurations” used by the Defense Department.
“This could potentially hamper U.S. warfighters at a critical point in time,” the filing said.
Last week, the DOD officially banned Anthropic’s technology and deemed the company a supply chain risk, a label that’s historically been reserved for foreign adversaries. The designation, which was effective immediately, will require defense vendors and contractors to certify that they don’t use Anthropic’s models in their work with the Pentagon.
Anthropic sued the Trump administration on Monday, calling the government’s actions “unprecedented and unlawful,” and claiming that they are “harming Anthropic irreparably,” putting hundreds of millions of dollars worth of contracts in jeopardy in the near term.
Microsoft’s comments on Tuesday appeared in a motion for a proposed amicus brief with the court. Amicus brief filings are submitted by parties that are not named in a given case, but that have relevant expertise or will be affected by the outcome.
In November, Microsoft announced plans to invest up to $5 billion in Anthropic. The company has also been a major investor in its rival OpenAI since 2019.
Anthropic had been renegotiating its contract with the DOD in recent weeks, but talks between the two organizations collapsed after they failed to agree on how its models, known as Claude, could be used.
Anthropic sought assurance that its models would not be used for fully autonomous weapons or domestic mass surveillance, while the DOD wanted the company to give the military unfettered access for all lawful purposes. Neither party budged.
Following the Pentagon’s announced ban, Microsoft and its top cloud rivals, Amazon and Google, all updated their customers, informing them that Anthropic’s products outside of defense work would remain accessible on their cloud platforms.
Microsoft said in the Tuesday filing that a temporary restraining order will allow Anthropic and the DOD to pursue a “negotiated resolution that will better serve all involved and avoid wide-ranging business impacts.”
“We believe everyone involved shares common goals, and we need time and a process to find common ground,” a Microsoft spokesperson said in a statement. “The Department of War 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.”
Anthropic was founded in 2021 by a group of former OpenAI executives, and it’s ballooned into one of the fastest-growing tech startups in the U.S., reaching a valuation of $380 billion.
–CNBC’s Dan Mangan and Lora Kolodny contributed to this report
WATCH: Why the U.S. Defense Department blacklist of Anthropic is so unprecedented
