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, which it promoted as offering “frontier-level coding intelligence.”

However, an X user posting under the name Fynn soon claimed that Composer 2 was “just Kimi 2.5” with additional reinforcement learning — Kimi 2.5 being 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 seemed to identify Kimi as the model.

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

It was a surprising revelation, since Cursor is a well-funded U.S. startup that raised a $2.3 billion round last fall at a $29.3 billion valuation, and is reportedly exceeding $2 billion in annualized 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 acknowledged , “Yep, Composer 2 started from an open-source base!” But he said, “Only ~1/4 of the compute spent on the final model came from the base, 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 the Kimi account on X repeated in a subsequent post congratulating Cursor , where it said the Cursor used Kimi “as part of an authorized commercial partnership” with Fireworks AI.

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“We are proud to see Kimi-k2.5 provide the foundation,” the Kimi account said. “Seeing our model integrated effectively through Cursor’s continued pretraining & high-compute RL training is the open model ecosystem we love to support.”

So why not acknowledge Kimi upfront? Beyond any potential embarrassment in not creating a model from scratch, building on top of a Chinese model might feel particularly fraught right now, with the so-called AI “arms race” often framed as an existential battle between United States and China . (See, for example, Silicon Valley’s apparent panic after Chinese company DeepSeek released a competitive model early last year.)

Cursor co-founder Aman Sanger acknowledged , “It was a miss to not mention the Kimi base in our blog from the start. We’ll fix that for the next model.”

Anthony Ha is TechCrunch’s weekend editor. Previously, he worked as a tech reporter at Adweek, a senior editor at VentureBeat, a local government reporter at the Hollister Free Lance, and vice president of content at a VC firm. He lives in New York City.

You can contact or verify outreach from Anthony by emailing anthony.ha@techcrunch.com .

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