Cursor admits Composer 2 based on Moonshot AI’s Kimi 2.5
Coding artificial intelligence company Cursor acknowledged its new Composer 2 model is based on Moonshot AI’s Kimi 2.5 after an X user identified Kimi code within the product.
was messing with the OpenAI base URL in Cursor and caught this
accounts/anysphere/models/kimi-k2p5-rl-0317-s515-fast
so composer 2 is just Kimi K2.5 with RL
at least rename the model ID https://t.co/MQOuEuF3Pd pic.twitter.com/fyUWbo1InF
— Fynn (@fynnso) March 19, 2026
The revelation prompted questions regarding transparency from Cursor, which had promoted Composer 2 as offering “frontier-level coding intelligence” without mentioning a third-party base model in its announcement.
Cursor’s Vice President of Developer Education Lee Robinson stated that Composer 2 “started from an open-source base,” but said only approximately “1/4 of the compute spent on the final model came from the base.” Robinson also stated Composer 2’s performance on benchmarks is “very different” from Kimi’s due to Cursor’s additional training.
Yep, Composer 2 started from an open-source base! We will do full pretraining in the future.
Only ~1/4 of the compute spent on the final model came from the base, the rest is from our training. This is why evals are very different.
And yes, we are following the license through… https://t.co/pEfuWAhIR1
— Lee Robinson (@leerob) March 20, 2026
The Kimi account on X confirmed the arrangement, stating Cursor used Kimi “as part of an authorized commercial partnership” with Fireworks AI. The Kimi account added it was “proud to see Kimi-k2.5 provide the foundation.”
Congrats to the @cursor_ai team on the launch of Composer 2!
We are proud to see Kimi-k2.5 provide the foundation. Seeing our model integrated effectively through Cursor's continued pretraining & high-compute RL training is the open model ecosystem we love to support.…
— Kimi.ai (@Kimi_Moonshot) March 20, 2026
Cursor co-founder Aman Sanger acknowledged, “It was a miss to not mention the Kimi base in our blog from the start.” Sanger added the company would address this for future models.
Cursor is a U.S. startup which raised $2.3 billion in fall 2023 at a $29.3 billion valuation. The company is reportedly exceeding $2 billion in annualized revenue. Moonshot AI is a Chinese company backed by Alibaba and HongShan.