Cursor Admits: Composer 2 is Based on Moonshot AI's Kimi Model

The American company Cursor, specializing in AI-driven coding, recently unveiled its latest model, Composer 2, touted for its advanced capabilities. However, a controversy erupted when a user on the social network X, going by the name Fynn, 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 known as Sequoia China.

Fynn backed up his claims by showing code that identified Kimi as the basis of the model, mocking Cursor by stating: "[A]t least rename the model ID." This revelation surprised many, especially since Cursor, a well-funded startup, raised a $2.3 billion round last fall, with an impressive valuation of $29.3 billion, and is reportedly exceeding $2 billion in annualized revenue. The company had not mentioned any link to Moonshot AI in its official announcement.

Lee Robinson, Vice President of Developer Education at Cursor, quickly confirmed that Composer 2 indeed relied on an open-source foundation. He clarified that only a quarter of the computing resources used for Composer 2 came from Kimi, with the rest stemming from Cursor's proprietary training. Robinson also emphasized that Composer 2's performance on various benchmarks is "very different" from that of Kimi.

Robinson insisted that the use of Kimi was in compliance with its licensing terms. The official Kimi account on X corroborated this statement, congratulating Cursor for its use of the model as part of an authorized commercial partnership with Fireworks AI. The Kimi account stated: "We are proud to see Kimi-k2.5 provide the foundation. Seeing our model effectively integrated through Cursor's ongoing pre-training and high-capacity reinforcement training is the open model ecosystem we love to support."

The question of why Cursor did not mention Kimi from the outset remains. Aman Sanger, co-founder of Cursor, admitted: "It was a mistake not to mention the Kimi base in our blog from the beginning. We will correct this for the next model." This omission may be linked to the current sensitivity surrounding Sino-American collaborations in the field of artificial intelligence, often viewed through the lens of strategic competition between the two nations.