AI coding company Cursor unveiled its new model, Composer 2, claiming it provides “frontier-level coding intelligence.” However, an X user named Fynn alleged that Composer 2 is merely “Kimi 2.5” with additional reinforcement learning, referencing Kimi 2.5 as an open-source model released by Moonshot AI, a Chinese company backed by Alibaba and HongShan. Fynn cited code that appeared to identify Kimi as the model, sarcastically suggesting a name change for the model ID.
The revelation was unexpected since Cursor, a U.S. startup, raised $2.3 billion last fall, valuing the company at $29.3 billion, with an estimated annualized revenue exceeding $2 billion. No mention of Moonshot AI or Kimi was made at the Composer 2 announcement.
Cursor’s VP of developer education, Lee Robinson, acknowledged that Composer 2 originated from an open-source base but clarified that only about one-quarter of the compute for the final model came from the base, with the rest from their training. Robinson stated that Composer 2’s performance on benchmarks significantly differed from Kimi’s.
Robinson emphasized that Cursor’s use of Kimi adhered to its license terms, a point supported by the Kimi account in a post celebrating Cursor’s use of Kimi as part of a commercial partnership with Fireworks AI. The Kimi account expressed pride in Kimi k2.5 serving as a foundation, acknowledging its integration with Cursor’s enhanced pretraining and extensive RL training as an ideal open model ecosystem.
Many questioned why Cursor didn’t initially credit Kimi, potentially due to the sensitivity of utilizing a Chinese model amid the AI “arms race” between the U.S. and China. Cursor co-founder Aman Sanger admitted the omission of mentioning Kimi in their blog was an oversight, promising to rectify it in the future.