Cursor, a U.S. startup known for its AI coding capabilities, has acknowledged that its new Composer 2 model was built on an open-source base from Moonshot AI’s Kimi, a revelation that has impacted perceptions of its frontier-level coding intelligence claims.
The news followed claims made by an X user, Fynn, who stated that Composer 2 was essentially “just Kimi 2.5” with additional reinforcement learning. Kimi 2.5 is an open-source model developed by Moonshot AI, a Chinese company backed by Alibaba and HongShan. This assertion raised questions about the originality and capabilities of Cursor’s Composer 2 model.
Lee Robinson, Cursor’s Vice President of Developer Education, confirmed that Composer 2 did indeed start from an open-source base. He clarified that approximately one-quarter of the compute for the final model originated from this base, while the remainder came from Cursor’s own training. Robinson emphasized that Composer 2’s performance on benchmarks is “very different” from Kimi’s, suggesting significant enhancements were made.
Robinson also maintained that Cursor’s use of Kimi complied with its licensing terms. The official Kimi account on X later congratulated Cursor, noting that its use of Kimi was “as part of an authorized commercial partnership” with Fireworks AI. The Kimi account stated, “We are proud to see Kimi-k2.5 provide the foundation.”
Aman Sanger, co-founder of Cursor, acknowledged that the company had initially omitted mentioning the Kimi base in their blog post. Sanger admitted, “It was a miss to not mention the Kimi base in our blog from the start. We’ll fix that for the next model.” This admission came as Cursor is valued at $29.3 billion following a $2.3 billion funding round last fall.
