What Cursor Released With Composer 2

Cursor launched a new model called Composer 2 and promoted it as delivering frontier-level coding intelligence.

The Claim That Composer 2 Was Really Kimi 2.5

After the launch, an X user posting under the name Fynn claimed Composer 2 was essentially Kimi 2.5, with additional reinforcement learning on top.

Kimi 2.5 is described as an open source model released by Moonshot AI, a Chinese company backed by Alibaba and HongShan (formerly Sequoia China).

What Was Pointed To As Evidence

Fynn pointed to code that appeared to identify Kimi as the model, along with the criticism that Cursor should have at least renamed the model ID.

Why The Situation Drew Attention

The claim stood out because Cursor is described as a well-funded U.S. startup. It reportedly:

  • raised a $2.3 billion round last fall at a $29.3 billion valuation
  • is reportedly exceeding $2 billion in annualized revenue

At the same time, Cursor didn’t mention Moonshot AI or Kimi in its announcement.

Cursor’s Response: Composer 2 Started From an Open-Source Base

Cursor’s vice president of developer education, Lee Robinson, acknowledged that Composer 2 started from an open-source base.

How Cursor Described The Compute Split

Robinson said that only ~1/4 of the compute spent on the final model came from the base, and the rest came from Cursor’s own training.

Cursor’s Position On Benchmark Performance Differences

Robinson also said that Composer 2’s performance on various benchmarks is very different from Kimi’s.

Licensing And Commercial Use Claims

Robinson said Cursor’s use of Kimi was consistent with the terms of its license.

Separately, the Kimi account on X repeated a related point in a subsequent post congratulating Cursor, saying Cursor used Kimi as part of an authorized commercial partnership with Fireworks AI.

The Kimi account also said it was proud to see Kimi-k2.5 provide the foundation, and framed the integration—through Cursor’s continued pretraining and high-compute RL training—as the kind of open model ecosystem it supports.

Why Cursor Didn’t Mention Kimi Up Front

One explanation raised is that, beyond any potential embarrassment about not building a model from scratch, building on a Chinese model could feel especially fraught right now, with an “AI arms race” often framed as a high-stakes competition between the United States and China.

Cursor Admits It Should Have Disclosed The Kimi Base

Cursor co-founder Aman Sanger acknowledged it was a mistake not to mention the Kimi base originally, saying it was “a miss” not to include it in the blog from the start, and that Cursor will fix that for the next model.