Key Points

• Anthropic sent a letter to U.S. officials accusing Alibaba of "brazenly" and "illicitly" attempting to extract its AI capabilities.
• The letter, which was obtained by CNBC, claims Alibaba carried out "the largest known distillation attack on Anthropic to date."
• Anthropic said operators affiliated with Alibaba and its AI lab carried out 28.8 million exchanges with its models using thousands of fraudulent accounts.

Anthropic sent a letter to the U.S. Senate Committee on Banking, Housing, and Urban Affairs accusing the Chinese tech company Alibaba of "brazenly" and "illicitly" attempting to extract its artificial intelligence capabilities, CNBC confirmed on Wednesday.

The letter, which was addressed to Sen. Tim Scott, R-S.C., and Sen. Elizabeth Warren, D-Mass., on June 10, said Alibaba carried out "the largest known distillation attack on Anthropic to date."

Distillation is an AI training method where a small, less capable model is built using outputs from an existing, stronger model.

Anthropic said operators affiliated with Alibaba and its AI lab carried out 28.8 million exchanges with its models using roughly 25,000 fraudulent accounts between April 22 and June 5, according to the letter, which was viewed by CNBC.

"We believe combating the threat of illicit distillation requires coordinated action between government and industry, and we will continue working with Congress and the Administration to maintain American AI leadership," an Anthropic spokesperson said in a statement.

A representative for Alibaba did not immediately respond to CNBC's request for comment.

The letter lands two months after the White House Office of Science and Technology Policy issued a memorandum that pledged to help AI companies detect and coordinate against industrial-scale distillation. Anthropic wrote that in proceeding with its distillation attacks, Alibaba "ignored the Trump Administration's warnings."

In February, Anthropic announced that it had identified three "industrial-scale" distillation campaigns from three other AI labs: DeepSeek, Moonshot and MiniMax. The company said in a blog post at the time that the campaigns were growing in intensity and sophistication, and it encouraged collaboration across the AI industry, cloud providers and policymakers.

But in recent weeks, Anthropic's work with policymakers has been complicated.

The company said earlier this month that it received an export control directive from the Trump administration ordering the company to suspend access to its latest Claude models, Fable 5 and Mythos 5, "by any foreign national, whether inside or outside the United States, including foreign national Anthropic employees."

The government cited "national security authorities" but didn't specify its concern, Anthropic said.

Senior staffers flew to Washington, D.C., to meet with members of the Trump administration over the next several days. The company told CNBC that "both parties are working quickly to get this resolved," but hasn't yet said when it expects its models to come back online.