Cursor "Shell Company" Kimi Controversy Reversal: From Copyright Allegations to Authorized Collaboration, China's Open-Source Models Become Global AI Foundation Again

Title: Cursor “Shells” Kimi Controversy Turns Around: From Infringement Doubts to Authorized Collaboration, China’s Open Source Models Reemerge as Global AI Foundations

Author: Thinking Weird

Source:

Repost: Mars Finance

Early morning on March 20, AI programming tool Cursor (parent company Anysphere, latest valuation $29.3 billion) released its self-developed model Composer 2. The blog stated that performance improvements came from “continuing pretraining on the base model, combined with reinforcement learning,” without mentioning the source of the base model.

Less than two hours later, developer @fynnso intercepted the actual model ID of Composer 2 while debugging Cursor API requests: kimi-k2p5-rl-0317-s515-fast, literally “Kimi K2.5 + RL.” Yue Zhi Anmian pretraining lead Du Yulun immediately tweeted, saying that after testing Composer 2’s tokenizer, they found it “completely identical to our Kimi tokenizer,” and “it can almost be confirmed that our model was further retrained,” directly questioning Cursor co-founder Michael Truell: “Why don’t you respect our license and pay any fees?”

The tweet was later deleted. The controversy quickly spread on social media, with Elon Musk replying under @fynnso’s post, “Yeah, it’s Kimi 2.5,” further amplifying the topic.

Kimi K2.5 uses a modified MIT license, explicitly stating: commercial products with over 100 million active users or monthly revenue exceeding $20 million must prominently display “Kimi K2.5” in the user interface. Given Cursor’s valuation and paying user base, the revenue threshold was almost certainly triggered.

Subsequently, the narrative shifted. The official account of Yue Zhi Anmian @Kimi_Moonshot posted early today, changing tone from accusation to congratulations: “Congratulations to the Cursor team on releasing Composer 2. We are proud to see Kimi K2.5 providing the foundation.” The statement also clarified that Cursor accesses Kimi K2.5 through Fireworks AI-hosted RL and inference platforms, which constitutes authorized commercial cooperation, with license compliance ensured through Fireworks AI’s commercial agreement.

Following Kimi’s official statement, Cursor co-founder Aman Sanger and VP of Developer Education Lee Robinson responded. Sanger explained the technical choices: the team evaluated multiple base models for perplexity, and Kimi K2.5 “proved to be the strongest,” then added continued pretraining and four times larger high-compute reinforcement learning, deploying via Fireworks AI’s inference and RL samplers.

Robinson added that about a quarter of the final model’s compute came from the base, with the remaining three-quarters from Cursor’s own training. Both admitted that not mentioning Kimi as the base in the blog post was a “mistake,” and promised that the next model would be clearly labeled from the start.

This is the second time Cursor has been found using a Chinese open-source model without disclosure. In November 2025, when Composer 1 was released, the community discovered its tokenizer matched DeepSeek, and the model occasionally output Chinese during inference, with no explanation from Cursor at the time.

The controversy has gone beyond license compliance. Hugging Face co-founder and CEO Clément Delangue commented that this is yet another validation of Chinese open source: “Today, Chinese open source is the biggest force shaping the global AI tech stack.” The frontier of competition is no longer just about who trains from scratch, but who can adapt, fine-tune, and productize the fastest.

A noteworthy coincidence: on March 15, Bloomberg reported that Yue Zhi Anmian was seeking up to $1 billion in a new funding round, with a valuation of about $18 billion—more than quadruple the valuation three months earlier, with Alibaba and Tencent participating. Just five days later, the world’s highest-valued AI programming tool was found to be based on Kimi K2.5. Anysphere, valued at $29.3 billion, identified Kimi K2.5 as the “strongest base” in its evaluation, building its core products on it—perhaps the most direct market endorsement of Yue Zhi Anmian’s technical capabilities.

Before this funding round is completed, the Cursor incident effectively showcased Kimi’s capabilities to developers worldwide. Whether the $18 billion valuation still undervalues Yue Zhi Anmian may need to be reconsidered.