Cursor acknowledges that its new coding model is built on Moonshot AI’s Kimi.

AI coding company Cursor launched a new model this week called Composer 2. Composer 2 was advertised as providing “the first level of coding intelligence.”

However, user X, posting under the name Fynn, soon claimed that Composer 2 was “just Kimi 2.5” with additional reinforcement learning. Kimi 2.5 is an open source model recently released by Moonshot AI, a Chinese company backed by Alibaba and HongShan (formerly Sequoia China).

As evidence, Fynn pointed to code that appeared to identify Kimi as a model.

“(A)at least change the model ID name.” They laughed.

This was surprising, as Cursor is a well-funded American startup that raised $2.3 billion in funding last fall at a $29.3 billion valuation and reportedly has annual revenues in excess of $2 billion. The company also made no mention of Moonshot AI or Kimi in its announcement.

But Lee Robinson, Cursor’s vice president of developer training, quickly admitted, “Yes, Composer 2 started on an open source foundation!” But, he said, “only a quarter of the compute used in the final model came from the base, the rest came from our training.” As a result, he said Composer 2’s performance in various benchmarks was “very different” from Kimi’s.

Robinson also argued that Cursor’s use of Kimi was consistent with the terms of the license, which X’s Kimi account reiterated in a follow-up post congratulating Cursor, saying Cursor used Kimi “as part of an approved commercial partnership” with Fireworks AI.

“Proud to see Kimi-k2.5 providing the foundation,” the Kimi account said. “Seeing our models integrate effectively with Cursor’s ongoing pre-training and high-performance RL training is the open model ecosystem we want to support.”

So why not acknowledge Kimmy in advance? Beyond the embarrassment of not being able to create a model from scratch, building on the Chinese model can feel especially challenging at a time when the so-called AI “arms race” is often framed as an existential war between the United States and China. (See, for example, the panic in Silicon Valley early last year after Chinese company DeepSeek launched a competing model.)

“It was a mistake not to mention the Kimi base on the blog from the beginning. We will fix that in the next model,” admitted Aman Sanger, co-founder of Cursor.