Discussion

• @fynnso Fynn on x

  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 [image]

• @quinnypig Corey Quinn on x

  Moonshot is being incredibly diplomatic here considering Cursor spelled “Kimi K2.5” as “continued pre-training and reinforcement learning.” The model ID was literally kimi-k2p5-rl-0317-s515-fast. They forgot to file the serial numbers off. Nailed it.

• @leerob Lee Robinson on x

  Since people really want me to say this: “KIMI K2.5” ‼️ Yes, that is the base we started from. And we are following the license through inference partner terms (e.g. Fireworks) I'm thankful for OSS models personally, good for the ecosystem.

• @teortaxestex @teortaxestex on x

  Class Notice how well they've played this. Engineers reacted, deleted tweets, the community did everything else, mounting pressure until Cursor attributed the model. No need for scandal. [image]

• @snwy_me @snwy_me on x

  can everyone shut the fuck up now and stop acting like cursor just stole a baby from a hospital lmfao

• @gergelyorosz Gergely Orosz on x

  Cursor keeps showing poor judgment with comms - behaving not like a $10B+ company, but like an early-stage startup Hikes prices for many enterprise customers without notice, or comms or transparency Big bang Composer 2.0 release w/o sharing that it's based on Kimi 2.5

• @yampeleg Yam Peleg on x

  I don't get why people go after cursor for fine tuning an open source model, this is exactly what they are for.

• @leerob Lee Robinson on x

  I'm a big believer in open source, especially as AI improves. It was a miss to not mention the Kimi base in our blog from the start. We'll fix that for the next model 🙏 Their team clarified our usage was licensed in the tweet below. https://x.com/...

• @amanrsanger Aman Sanger on x

  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

• @timhaldorsson Tim Haldorsson on x

  Cursor wrapped the kimi model and called it their own model this is the beauty of open-source that you can just build and ship things

• @sundeep Sunny Madra on x

  The technology ecosystem has made significant progress by building upon open-source, great to see this continuing.

• @leerob Lee Robinson on x

  Here's confirmation the license is correct from the Kimi team. Agree with the feedback we should have mentioned the base up front, we will do that for the next model! https://x.com/...

• @clementdelangue Clem on x

  Looks like it's confirmed Cursor's new model is based on Kimi! It reinforces a couple of things: - open-source keeps being the greatest competition enabler - another validation for chinese open-source that is now the biggest force shaping the global AI stack - the frontier is no

• @yuchenj_uw Yuchen Jin on x

  People dunk on Cursor like: “it's just Kimi K2.5,” “look inside, it's a Chinese model.” There's no shame in building on top of strong base models and doing your own post-training or RL (as long as you respect the license). In most cases you don't need to pretrain from scratch.

• @elonmusk Elon Musk on x

  @fynnso Yeah, it's Kimi 2.5

• @ns123abc Nik on x

  🚨NEWS: Cursor's $50B “in-house model” is literally Kimi K2.5 with RL on top. Got caught in 24 hours >be Moonshot AI >spend hundreds of millions training Kimi K2.5 >1 trillion parameters, 15 trillion tokens, agent swarm architecture >beat GPT-5.2 and Opus 4.5 on real benchmarks [i…

• @cryptopunk7213 @cryptopunk7213 on x

  lmfao the new cursor model is actually a chinese model (kimi k2.5) they didn't even change the model name 😂 [image]

• @yuchenj_uw Yuchen Jin on x

  Cursor's Composer 2 is likely built on Kimi K2.5. The model URL + tokenizer are strong signals. I love this direction: companies mid-train and post-train on top of OSS LLMs. Prediction: open-source model labs will monetize by taking a cut when others build on top of their

• @leerob Lee Robinson on x

  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

• @auchenberg Kenneth Auchenberg on x

  So let me get this right: 1. MoonshotAI distills Claude from Anthropic with 3.4 million exchanges on their API. 2. Releases Kimi K2.5 as OSS. 3. Cursor RL fine-tunes Kimi K2.5 into Composer 2 Cursor now delivers Opus 4.6 performance for a fraction of the price. [image]

• @thdxr Dax on x

  whether this is true or not it's going to cause every company producing open source models to re-evaluate if they should continue to do so that is incredibly frustrating

• @jenzhuscott Jen Zhu on x

  The responses from @Kimi_Moonshot & @cursor_ai both are gracious. So wonderful to see. 1. There is absolutely no shame in building on top of open source model. Way better than repeating the same stacks in walled garden. Open-source > closed 2. Chinese open source models are [imag…

• @tmychow Trevor on x

  “1/4 of the compute spent on the final model came from the base, the rest is from our training” k2 and k2.5 (a continued pretrain of k2) each used 15T tokens k2 is 32B active; by 6np, kimi did 5.76e+24 flops if that's 1/4, cursor did 1.7e25 flops i.e. same as gpt-4 flops