According to 1M AI News, developer @fynnso discovered while debugging Cursor API requests that the actual model ID for Composer 2 is `kimi-k2p5-rl-0317-s515-fast`, literally meaning "Kimi K2.5 + RL." Shortly after, Yulun Du (@Yulun_Du), head of pretraining at Moonshot AI, tweeted that after testing Composer 2’s tokenizer, they found it to be "identical to our Kimi tokenizer" and "almost certainly the result of further fine-tuning of our model." He directly tagged Cursor co-founder Michael Truell, asking, "Why aren’t you respecting our license, or paying any fees?"
When Cursor 3 released Composer 2 on March 19, it attributed the performance improvements to "the first continued pre-training of a base model, combined with reinforcement learning," but made no mention of Kimi K2.5. These two points are not contradictory: continued pre-training and RL are inherently applied to some base model; Cursor simply did not disclose the source of the base model.
Kimi K2.5 uses a modified MIT license, which explicitly states: commercial products with over 100 million monthly active users or monthly revenue exceeding $20 million must prominently display "Kimi K2.5" in the user interface. Given Cursor's $29.3 billion valuation and paid user base, the monthly revenue threshold is almost certainly triggered. As of publication, Cursor has not publicly responded.
Moonshot AI Accuses Cursor of Using Kimi K2.5 Without License Compliance
ChainthinkShare
Summary
Moonshot AI’s Yulun Du has accused Cursor of using its Kimi K2.5 model in Composer 2 without proper compliance with AI + crypto news licensing requirements. A developer discovered the model ID `kimi-k2p5-rl-0317-s515-fast`, linking Composer 2 to Kimi K2.5. Moonshot claims Cursor reused the same tokenizer and may have trained on its model. Cursor cited pre-training and reinforcement learning as the basis for improvements but did not mention Kimi K2.5. The model’s license requires prominent labeling for products with high revenue or user volume—conditions that likely apply here. Cursor has not responded.
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