Cursor admits its new coding model was built on to...

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.” 

Nevertheless, an X person posting underneath the title Fynn soon claimed that Composer 2 was “simply Kimi 2.5” with extra reinforcement studying — Kimi 2.5 being an open source model recently released 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 round last fall at a $29.3 billion valuation, and is reportedly exceeding $2 billion in annualized revenue. Additionally, the corporate didn’t point out something about Moonshot AI or Kimi in its announcement.

Nevertheless, Cursor’s vp of developer schooling Lee Robinson soon acknowledged, “Yep, Composer 2 began from an open-source base!” However he stated, “Solely ~1/4 of the compute spent on the ultimate mannequin got here from the bottom, the remaining is from our coaching.” Because of this, he stated Composer 2’s efficiency on varied benchmarks is “very totally different” from Kimi’s.

Robinson additionally insisted that Cursor’s use of Kimi was in line with the phrases of its license, a degree the Kimi account on X repeated in a subsequent post congratulating Cursor, the place it stated the Cursor used Kimi “as a part of a certified business partnership” with Fireworks AI.

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

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 would possibly really feel notably fraught proper now, with the so-called AI “arms race” usually framed as an existential battle between United States and China. (See, for instance, Silicon Valley’s apparent panic after Chinese company DeepSeek released a competitive model early final yr.)

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 following mannequin.”