Microsoft-backed (MSFT) OpenAI has warned US Congress members that Chinese AI startup DeepSeek is trying to reverse engineer its large language models and use them to train their own software, Reuters reported Thursday, citing a memo.

The company accused DeepSeek of using a method called distillation as part of "ongoing efforts to free-ride on the capabilities developed by OpenAI and other US frontier labs."

"We have observed accounts associated with DeepSeek employees developing methods to circumvent OpenAI's access restrictions and access models through obfuscated third-party routers and other ways that mask their source," the memo said, according to news outlets.

Microsoft owns a major minority stake in OpenAI.

OpenAI, DeepSeek and its parent company High-Flyer did not immediately reply to MT Newswires' requests for comment.