Cursor admits its new coding model was built on Moonshot AI’s Kimi

AI coding company Cursor released a new model this week called Composer 2, which promoted as offering “edge-level encryption intelligence.”

However, a user soon claimed that Composer 2 was “just Kimi 2.5” with additional reinforcement learning: Kimi 2.5 was an open source model recently released by Moonshot AIa Chinese company backed by Alibaba and HongShan (formerly Sequoia China).

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

“(At least change the name of the model ID,” they scoffed.

It was a surprising revelation, as Cursor is a well-funded American startup that raised a $2.3 billion round last fall with a valuation of $29.3 billion, and is Reportedly Exceeds $2 Billion in Annualized Revenue. Additionally, the company did not mention anything about Moonshot AI or Kimi in its announcement.

However, Cursor’s vice president of developer education Lee Robinson soon recognized“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 baseline, the rest is from our training.” As a result, he said Composer 2’s performance on various benchmarks is “very different” from Kimi’s.

Robinson also insisted that Cursor’s use of Kimi was consistent with the terms of its license, a point Kimi’s X account repeated in a later post congratulating Cursorwhere it said Cursor used Kimi “as part of a licensed commercial partnership” with Fireworks AI.

“We are proud to see Kimi-k2.5 providing the foundation,” Kimi’s account read. “Seeing our model integrated effectively through Cursor’s continuous pre-training and high-computation RL training is the open model ecosystem we love to support.”

So why not acknowledge Kimi from the beginning? Beyond any potential embarrassment over not creating a model from scratch, building on a Chinese model may prove particularly complicated right now, with the so-called AI “arms race” often framed as An existential battle between the United States and China.. (See, for example, the case of Silicon Valley Apparent panic after Chinese company DeepSeek launches competitive model beginning of last year.)

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