Three hours after Cursor announced Composer 2 on March 19, a developer named Fynn was debugging an API call and noticed something the company hadn’t mentioned: the model was returning the identifier kimi-k2p5-rl-0317-s515-fast. The name belongs to Kimi K2.5, an open-source model built by Moonshot AI, a Chinese startup currently valued at around $18 billion. Fynn posted the screenshot. It got 444,000 views. Elon Musk replied: “Yeah, it’s Kimi 2.5.”
Cursor had promoted Composer 2 as a model that beats Claude Opus 4.6 at one-tenth of the price, achieved through “continued pre-training and reinforcement learning.” The blog post made no mention of any base model. The company is currently in talks to raise funding at a $50 billion valuation, up from $29.3 billion just four months ago. Its annualized revenue exceeded $2 billion as of February.
What Cursor Actually Built
Co-founder Aman Sanger posted a response the following day: “Not mentioning the Kimi base model from the start in the blog was our oversight, and we will correct this in the next model.” He said the team evaluated multiple base models and Kimi K2.5 “proved to be the strongest,” then applied additional pre-training and high-compute reinforcement learning. VP of Developer Education Lee Robinson added that roughly one-quarter of the final model’s compute came from Kimi K2.5, and three-quarters from Cursor’s own training.
Kimi K2.5’s modified MIT license requires any commercial product generating more than $20 million per month in revenue to prominently display “Kimi K2.5” on its interface. Cursor’s revenue comfortably exceeds that threshold. The product shipped as “Composer 2.” Moonshot AI’s official account ultimately landed on goodwill: “Proud to see Kimi K2.5 being used as a base model. This is the open-source ecosystem we love.” The company’s pre-training lead, Du Yulun, withdrew earlier questions about unpaid usage after it emerged Cursor accesses the model through Fireworks AI, an authorized commercial partner.
The Inconvenient Geography
This was not Cursor’s first brush with Chinese model suspicions. In October 2025, users noticed that code generated by Composer 1 occasionally contained Chinese-language comments — a detail that sparked similar speculation about the model’s origins. The company did not address those concerns at the time.
The broader pattern is difficult to ignore. The US government has spent years imposing chip export controls and sanctions designed to slow Chinese AI development. The restrictions have denied Chinese labs access to Nvidia’s most powerful chips. And yet Moonshot AI, DeepSeek, and others have continued producing models that American companies quietly integrate into their products. Hugging Face CEO Clement Delangue put it plainly this week: “Chinese open-source models have now become the greatest force shaping the global AI tech stack.”
The Competitor That Moved Faster
Windsurf, a direct Cursor competitor, announced free access to Kimi K2.5 for a week in the days following the controversy — framing the episode as a marketing opportunity rather than a liability. The contrast with Cursor’s handling was pointed. Where Cursor shipped the model without attribution and scrambled to explain afterward, Windsurf put the Chinese model’s name in the headline.
Cursor’s co-founder said the omission would be corrected in the next release. The company has not indicated whether it plans to update the current Composer 2 interface to meet Kimi K2.5’s license requirements retroactively.