Cursor admits its new coding mannequin was constructed on prime of Moonshot AI’s Kimi

AI coding firm Cursor launched a brand new mannequin this week referred to as Composer 2, which it promoted as providing “frontier-level coding intelligence.” 

Nonetheless, an X person posting underneath the identify Fynn soon claimed that Composer 2 was “simply Kimi 2.5” with extra reinforcement studying — Kimi 2.5 being an open supply mannequin lately launched by Moonshot AI, a Chinese language firm backed by Alibaba and HongShan (previously Sequoia China). 

As proof, Fynn pointed to code that appeared to determine Kimi because the mannequin.

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

It was a stunning revelation, since Cursor is a well-funded U.S. startup that raised a $2.3 billion spherical final fall at a $29.3 billion valuation, and is reportedly exceeding $2 billion in annualized income. Additionally, the corporate didn’t point out something about Moonshot AI or Kimi in its announcement.

Nonetheless, Cursor’s vp of developer training Lee Robinson soon acknowledged, “Yep, Composer 2 began from an open-source base!” However he mentioned, “Solely ~1/4 of the compute spent on the ultimate mannequin got here from the bottom, the remainder is from our coaching.” Consequently, he mentioned Composer 2’s efficiency on numerous benchmarks is “very totally different” from Kimi’s.

Robinson additionally insisted that Cursor’s use of Kimi was according to the phrases of its license, some extent the Kimi account on X repeated in a subsequent post congratulating Cursor, the place it mentioned the Cursor used Kimi “as a part of a certified industrial partnership” with Fireworks AI.

“We’re proud to see Kimi-k2.5 present the muse,” the Kimi account mentioned. “Seeing our mannequin built-in successfully by means of Cursor’s continued pretraining & high-compute RL coaching is the open mannequin ecosystem we like to help.”

So why not acknowledge Kimi upfront? Past any potential embarrassment in not making a mannequin from scratch, constructing on prime of a Chinese language mannequin may really feel significantly fraught proper now, with the so-called AI “arms race” typically framed as an existential battle between United States and China. (See, for instance, Silicon Valley’s obvious panic after Chinese language firm DeepSeek launched a aggressive mannequin early final 12 months.)

Cursor co-founder Aman Sanger acknowledged, “It was a miss to not point out the Kimi base in our weblog from the beginning. We’ll repair that for the subsequent mannequin.”