US AI company Anthropic accused Alibaba, the Chinese technology and e-commerce giant, of illicitly extracting its Claude AI model capabilities in what ​it said was the largest known attack of its kind on the company, according to a ‌letter seen by Reuters.

The strike by Alibaba is described as a “distillation” effort, which Anthropic has said involves training a less capable model on the outputs of a stronger one.

Anthropic said the campaign was conducted between April 22 and June 5, 2026, and generated more ​than 28.8 million exchanges with Claude through almost 25,000 fraudulent accounts.

Anthropic said in the letter that ​distillation is a way to help accelerate China’s ability to reach Anthropic’s advanced Mythos ⁠Preview capabilities.

It said the campaign was conducted by operators affiliated with Alibaba and Alibaba Qwen, Alibaba’s AI lab. ​Alibaba did not immediately respond to a request for comment.

The letter, dated June 10, was sent to Senators Tim ​Scott and Elizabeth Warren, the chair and ranking member, respectively, of the US Senate Banking Committee, ahead of a scheduled hearing on AI.

In April, the White House accused China of stealing US AI labs’ intellectual property on an industrial scale.

Anthropic said in the ​letter it was supportive of the US government’s efforts to combat the attacks, including partnering with private sector ​AI companies through threat-intelligence sharing and other exercises.

Anthropic said in a February posting that it had identified a campaign by Chinese AI ‌startup ⁠DeepSeek — whose low-cost AI model sent shockwaves through the technology world in January 2025 — and two other Chinese AI labs to illicitly extract capabilities from its Claude AI platform.

It said DeepSeek’s operation involved over 150,000 exchanges, while Moonshot AI was at a scale of over 3.4 million and MiniMax over 13 million.

It also said at the ​time that the campaigns were ​growing in “intensity and sophistication” ⁠and that addressing the threat would require “rapid, coordinated action among industry players, policymakers and the global AI community”.

Alibaba was added to the Pentagon’s Chinese military companies list this ​month, a designation it is challenging.

But the Commerce Department has held off placing DeepSeek on ​a trade blacklist, ⁠as Reuters exclusively reported this month, despite it being deemed a national security risk by an interagency governmental committee, as the department tries to avoid escalating tensions with Beijing.

Meanwhile, on June 12, two days after Anthropic sent the ⁠letter, the ​Commerce Department imposed controversial restrictions on Anthropic’s latest Mythos and Fable ​AI models because officials feared they could be deployed by military intelligence users in China and other countries of concern. The restrictions resulted in ​Anthropic disabling access to the models globally.