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.

- Patricia Clarke Technology reporter

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.