Cursor, an AI coding company, introduced a new model this week named Composer 2, which it described as delivering "frontier-level coding intelligence."

EMBED_PLACEHOLDER_0

Shortly after, an X user known as Fynn asserted that Composer 2 was essentially "just Kimi 2.5" enhanced with additional reinforcement learning. Kimi 2.5 is an open-source model recently launched by Moonshot AI, a Chinese firm supported by Alibaba and HongShan (previously Sequoia China). As proof, Fynn highlighted code that appeared to identify Kimi as the underlying model. "[A]t least rename the model ID," they remarked dismissively.

This was a notable claim, given that Cursor is a well-financed U.S. startup that secured a $2.3 billion funding round last autumn, achieving a $29.3 billion valuation. The company is also reported to be generating over $2 billion in annualized revenue. Notably, Cursor's initial announcement made no reference to Moonshot AI or Kimi.

However, Lee Robinson, Cursor's vice president of developer education, later confirmed, "Yep, Composer 2 started from an open-source base." He clarified that "Only ~1/4 of the compute spent on the final model came from the base, the rest is from our training." Consequently, he stated that Composer 2's performance across various benchmarks is "very different" from Kimi's.

Robinson further emphasized that Cursor's utilization of Kimi complied with its licensing terms. This point was echoed by the Kimi account on X in a follow-up post congratulating Cursor, which noted that Cursor employed Kimi "as part of an authorized commercial partnership" with Fireworks AI. "We are proud to see Kimi-k2.5 provide the foundation," the Kimi account stated. "Seeing our model integrated effectively through Cursor’s continued pretraining & high-compute RL training is the open model ecosystem we love to support."

This raises the question: why wasn't Kimi acknowledged from the beginning? Beyond any potential discomfort in not developing a model entirely from scratch, building upon a Chinese model may seem especially sensitive at present. The so-called AI "arms race" is frequently portrayed as a critical competition between the United States and China—evident, for instance, in Silicon Valley's apparent concern following Chinese company DeepSeek's release of a competitive model early last year.

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