The Pentagon has told its senior leaders that use of Anthropic's AI tools may continue beyond a previously announced six-month phase-out period ​if deemed critical to national security, according to an internal memo ‌seen by Reuters.

The memo is dated March 6 and signed by Pentagon Chief Information Officer Kirsten Davies. It says the exemptions can be authorized "in rare and extraordinary circumstances" and "will only ​be considered for mission-critical activities directly supporting national security operations where no ​viable alternative exists."

Any Pentagon unit seeking an exemption must submit a ⁠comprehensive risk mitigation plan for approval, according to the document, first reported by ​CBS News.

The Pentagon confirmed the memo but declined to comment further. Anthropic did ​not immediately respond to a request for comment.

An expert said the carve-out signals how challenging it will be to implement the ban on Anthropic.

The memo is a "recognition of the fact that ​it's really hard for most vendors to certify they have removed the company ​from the entirety of their supply chain," said Franklin Turner, a government contracts lawyer at McCarter & ‌English. ⁠For instance, contractors may find it difficult to ensure their software is free of any open-source code originating from Anthropic, he said.

"I do expect to see a flurry of waiver requests," he added.

The memo comes after a heated weeks-long dispute ​over technology guardrails on ​use of Anthropic's ⁠AI tools by the military that culminated in Defense Secretary Pete Hegseth labeling the firm a supply chain risk and ​banning its use by the Pentagon and its contractors.

Anthropic filed ​a lawsuit ⁠on Monday to block the Pentagon from implementing the ban.

The memo also directed officials to prioritize removing Anthropic's products from systems supporting critical missions, such as nuclear weapons and ⁠ballistic ​missile defense.

The memo also reaffirmed that the ban ​extends to defense contractors. It gives Pentagon contracting officers 30 days to notify contractors, which must then ​certify full compliance by the 180-day deadline.