HomeCursor acknowledges its new coding model is built on Moonshot AI's Kimi
Cursor, an AI coding company, unveiled a new model this week called Composer 2, which it promoted as offering "frontier-level coding intelligence."
However, an X user who goes by 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.
"At least rename the model ID," they scoffed.
This revelation was surprising, given that Cursor is a well-funded U.S. startup that raised $2.3 billion in a round last fall at a $29.3 billion valuation, and reportedly exceeds $2 billion in annualized revenue. Moreover, the company made no mention of 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 added, "Only about a quarter of the compute spent on the final model came from the base; the rest came 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 complied with the terms of its license, a point that the Kimi account on X echoed in a subsequent post congratulating Cursor, in which it stated that Cursor used 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 said. "Seeing our model integrated effectively through Cursor's continued pretraining and high-compute RL training is the open model ecosystem we love to support."
So why didn't the company acknowledge Kimi upfront? Beyond any potential embarrassment of not creating a model from scratch, building on a Chinese model might feel particularly risky right now, given that the so-called AI "arms race" is often framed as an existential battle between the 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 not to mention the Kimi base in our blog from the start. We'll fix that for the next model."
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Cursor, an AI coding company, unveiled a new model this week called Composer 2, which it promoted as offering "frontier-level coding intelligence."
However, an X user who goes by 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.
"At least rename the model ID," they scoffed.
This revelation was surprising, given that Cursor is a well-funded U.S. startup that raised $2.3 billion in a round last fall at a $29.3 billion valuation, and reportedly exceeds $2 billion in annualized revenue. Moreover, the company made no mention of 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 added, "Only about a quarter of the compute spent on the final model came from the base; the rest came 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 complied with the terms of its license, a point that the Kimi account on X echoed in a subsequent post congratulating Cursor, in which it stated that Cursor used 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 said. "Seeing our model integrated effectively through Cursor's continued pretraining and high-compute RL training is the open model ecosystem we love to support."
So why didn't the company acknowledge Kimi upfront? Beyond any potential embarrassment of not creating a model from scratch, building on a Chinese model might feel particularly risky right now, given that the so-called AI "arms race" is often framed as an existential battle between the 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 not to mention the Kimi base in our blog from the start. We'll fix that for the next model."
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