Cursor 'sshell' Kimi wind turned around: from tort questions to authorized cooperation, the Chinese open source model became the global AI base

In the early hours of March 20th, the AI programming tool Cursor (the parent company, Anysphere, latest estimate, $29.3 billion) published a self-study model Composer 2, which the blog describes as an upgrade from "first continuous pre-training of the base model, combined with enhanced learning", without reference to the base source。

Less than two hours later, the developer @fynnso intercepted the actual model COMposer 2 ID: `kimi-k2p5-rl-0317-s515-fast', literally "Kimi K2.5 + RL". Du Yullon, the head of the dark side training programme of the moon, immediately pushed, stating that the team tested Composer 2’s tokenizer found that “it was exactly the same as our Kimi tokenizer”, that “it was almost possible to confirm that our model was the result of further training”, and directly questioned the co-founder of Cursor, Michael Truell, “Why not respect our license and pay no fee.”。

The tweet was subsequently deleted. The controversy fermented rapidly in social media, and Elon Musk responded to "Yeah, it's Kimi 2.5" under @fynnso post, further widening the topic。

Kimi K2.5 uses the modified MIT protocol to specify that commercial products that exceed 100 million dollars per month or 20 million dollars per month must be clearly labelled as "Kiki K2.5" in the user interface. With Cursor ' s valuation and the size of the paid user, the monthly collection threshold is almost inevitable。

Then the wind turned around. The dark-faced official account number of the moon @Kimi Moonshot wrote this morning, and the tone shifted from accusations to congratulations: congratulations to Cursor for issuing Composer 2, "We are proud to see Kimi K2.5 provide the basis." The statement also clarified that Cursor ' s access to Kimi K2.5, through the RL hosted by Fireworks AI and the Delineation Platform, was authorized as commercial cooperation and that compliance with the licence was guaranteed by the Commercial Agreement of Fireworks AI。

After Kimi's official statement, Cursor co-founder Aman Singer followed up with Lee Robinson, Vice-President of Development Education. Singer explains the technical choice: the team conducted a puzzle assessment of the many bases, Kimi K2.5 "proved the best" and then added pre-training and four-fold high-calculation intensive learning, which was deployed with the RL sampler through the reasoning of Fireworks AI。

Robinson adds that the final model has about a quarter of the base's calculus and the remaining three quarters of Cursor's own training. Both admitted that Kimi's base "was a mistake" when the blog was published, indicating that the next model would be posted at the first time。

This is the second time that Cursor has been found using the open source model in China without disclosure. When Composer 1 was released in November 2025, the community found that its tokenizer was consistent with DeepSeek, and the model occasionally exported Chinese during the reasoning process, which was also not explained by Cursor。

This has led to discussions that go beyond licensing compliance itself. Hugging Face, co-founder and CEO Clément Delangue, commented that this was yet another validation of China’s open source, which “is now the greatest force in shaping the global AI technology warehouse”, and that the front-line competition is no longer just who trains from the beginning, but who is the fittest, fine-tuned, and the fastest to produce。

On March 15, Bloomberg reported that the dark side of the month was looking for a new round of financing of up to $1 billion, valued at about $18 billion, more than four times as much as three months ago, with Ali Baba and Zentte taking part in the bets. Only five days later, the highest-valued AI programming tool was found to be based on Kimi K2.5. Anyshere, valued at $29.3 billion, identified Kimi K2.5 as the “most powerful base” above which it built its core product, perhaps the most direct market endorsement for the dark side of the moon。

On the unfinished point of this round of finance, the Cursor event was tantamount to a global demonstration of the ability of Kimi to developers, and whether the $18 billion estimate still underestimates the dark side of the month might need to be revisited。