AI coding company Cursor has admitted that its latest model, Composer 2, is built on top of Moonshot AI’s open-source Kimi 2.5. Despite being a well-funded U.S. startup valued at $29.3 billion, Cursor failed to mention this in their announcement.

The revelation came from an X user named Fynn who pointed out code identifying the base model as Kimi. In response, Cursor’s vice president of developer education Lee Robinson acknowledged that Composer 2 started with a base but insisted only about one quarter of its compute was derived from it, stressing significant additional training and performance differences.

This case highlights the growing importance of open-source models in AI development while raising questions about transparency. Given the geopolitical tension surrounding AI innovation between the U.S. and China, Cursor’s decision not to acknowledge Kimi upfront might be seen as both strategic and potentially problematic.

Cursor co-founder Aman Sanger admitted it was a “miss” not to mention the base in their initial announcement but promised to correct this for future models. The incident also brings into question why such a high-profile company would rely on open-source models, especially from a competitor like Moonshot AI.

The Kimi account responded positively, congratulating Cursor and emphasizing their support of the open model ecosystem. However, the backlash could impact how Cursor and other companies approach using external models in their products moving forward.