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

AI coding company Cursor launched a new model this week called Composer 2 promoted as offering “border-level coding intelligence.”

However, an X user posts 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 the model.

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

It was a surprising revelation, considering Cursor is a well-funded U.S. startup that raised a $2.3 billion investment round last fall at a $29.3 billion valuation, and reportedly has more than $2 billion in annual revenue. The company also didn’t mention anything about Moonshot AI or Kimi in its announcement.

However, Cursor’s vice president of developer education Lee Robinson quickly admitted it“Yes, Composer 2 started from an open source foundation!” But he said: “Only ~1/4 of the computing power spent on the final model came from scratch, the rest comes from our training.” As a result, he said Composer 2’s performance on several benchmarks is “very different” from Kimi’s.

Robinson also emphasized that Cursor’s use of Kimi was in accordance with the terms of its license, a point the Kimi account on subsequent post congratulating Cursorwhere it stated that Cursor was using Kimi “as part of an authorized commercial partnership” with Fireworks AI.

“We are proud that Kimi-k2.5 is the foundation,” the Kimi account said. “Effectively integrating our model through Cursor’s continuous pre-training and high-compute RL training is the open model ecosystem we are excited to support.”

So why not acknowledge Kimi up front? Putting aside any embarrassment from not creating a model from scratch, building on a Chinese model can feel particularly fraught right now, with the so-called AI “arms race” often portrayed as an existential battle between the United States and China. (See, for example, the apparent panic in Silicon Valley after the Chinese company DeepSeek launched a competitive model early last year.)

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