Cursor admits that his new coding model was built on top of Moonshot AI’s Kimi

AI coding company Cursor introduced a new model this week called Composer 2, which are promoted as it offers “borderline coding intelligence”.

However, a user X posts under the name Fynn he soon claimed that Composer 2 was “just Kimi 2.5” with reinforcement learning added — 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 proof, Fynn showed the code that seemed to identify Kimi as the model.

“[A]At least rename the model ID,” they scoffed.

It was a surprising revelation, as Cursor is a well-funded US startup that raised $2.3 billion last fall at a $29.3 billion valuation and is reportedly over $2 billion in annual revenue. Also, the company didn’t mention anything about Moonshot AI or Kimi in its announcement.

However, Cursor’s vice president of developer education Lee Robinson soon recognized this“Yes, Composer 2 started from an open source base!” But he said, “Only ~1/4 of the computation spent on the final model came from the base, the rest is from our training.” As a result, he said the Composer 2’s performance in various benchmarks is “very different” to Kimi’s.

Robinson also insisted that Cursor’s use of Kimi was consistent with the terms of its license, a point Kimi’s account on X reiterated in a next post congratulations cursorwhere it stated that Cursor used Kimi “as part of an authorized commercial partnership” with Fireworks AI.

“We are proud to see Kimi-k2.5 provide the foundation,” the Kimi account said. “Seeing our model integrate effectively through ongoing Cursor pre-training and highly computational RL training is the open model ecosystem we love to support.”

So why not recognize Kimi in advance? Beyond any potential embarrassment of not building a model from scratch, building on a Chinese model can feel especially difficult right now, with the so-called AI “arms race” often framed as an existential battle between the United States and China. (See, for example, Silicon Valley’s apparent panic after Chinese company DeepSeek launched a competing model early last year.)

Cursor co-founder Aman Sanger recognized“It was a mistake not to mention the Kimi base on our blog from the beginning. We will fix this for the next model.”