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Cursor AI Founder Reveals Kimi k2.5 as Foundation for Composer-2

Cursor AI Founder Reveals Kimi k2.5 as Foundation for Composer-2

@amanrsanger

We've evaluated a lot of base models on perplexity-based evals and Kimi k2.5 proved to be the strongest!

After that, we do continued pre-training and high-compute RL (a 4x scale-up).

The combination of the strong base, CPT and RL, and Fireworks' inference and RL samplers make Composer-2 frontier level.

It was a miss to not mention the Kimi base in our blog from the start. We'll fix that for the next model.

!Image 3: Kimi.ai

#### Kimi.ai

@Kimi_Moonshot · 9h ago

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.

Note: Cursor accesses Kimi-k2.5 via @FireworksAI_HQ ' hosted RL and inference platform as part of an authorized commercial partnership.Show More

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Mar 20, 2026, 7:41 PM View on X

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241.1K Views  Aman Sanger @amanrsanger

One Sentence Summary

Cursor AI founder reveals that Kimi k2.5 was the strongest base model in their evaluations, and after continued pre-training and high-compute RL, Composer-2 achieved frontier-level performance.

Summary

Aman Sanger, founder of Cursor AI, discloses the technical foundation behind their new Composer-2 model. The team evaluated numerous base models using perplexity-based evaluations, and Kimi k2.5 emerged as the strongest. They then applied continued pre-training (CPT) and high-compute reinforcement learning (RL) at 4x scale. The combination of Kimi's strong base model, CPT, RL, and Fireworks' inference and RL samplers enabled Composer-2 to reach frontier-level performance. Sanger acknowledges it was an omission not to mention the Kimi base in their original blog post and promises to correct this for the next model release.

AI Score

84

Influence Score 315

Published At Yesterday

Language

English

Tags

Cursor AI

Composer-2

Kimi k2.5

AI Coding

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Cursor AI Founder Reveals Kimi k2.5 as Foundation for Com...