According to 1M AI News monitoring, developer @fynnso discovered during debugging of the Cursor API request that the actual model ID for Composer 2 is `kimi-k2p5-rl-0317-s515-fast`, literally meaning "Kimi K2.5 + RL". Yulun Du (@Yulun_Du), Pre-training Lead at Moonshot AI, immediately tweeted that after testing Composer 2’s tokenizer, they found it "completely identical to our Kimi tokenizer," and stated, "it is almost certain this is our model further fine-tuned via post-training," directly tagging Cursor co-founder Michael Truell and questioning, "Why aren't you respecting our license, and why have you paid no fees?"

When Cursor launched Composer 2 on March 19, they claimed performance improvements stemmed from "first conducting continued pre-training on the base model, followed by reinforcement learning"—but never mentioned Kimi K2.5. These points are not contradictory: continued pre-training and RL inherently occur on top of a base model, and Cursor simply omitted disclosure of the base model's origin.

Kimi K2.5 is licensed under a modified MIT license, which explicitly states that commercial products with over 100 million monthly active users or over $20 million in monthly revenue must prominently display "Kimi K2.5" in the user interface. Given Cursor’s $29.3 billion valuation and its paying user base, the revenue threshold is almost certainly triggered. As of this writing, Cursor has not issued any public response.