What do you mean by “pure language model”? The reasoning step is still just the LLM spitting out tokens and this was confirmed by Deepseek replicating the o models. There’s not also a proof verifier or something similar running alongside it according to the openai researchers.
If you mean pure as in there’s not additional training beyond the pretraining, I don’t think any model has been pure since gpt-3.5.
Local models you can get just the pretrained versions of, no RLHF. IIRC both Llama and Gemma make them available.
Reason? Maybe. But there's one limitation that we currently have no idea how to overcome; LLMs don't know how much they know. If they tell you they don't something it may be a lie. If they tell you they do, this may be a lie too. I, a human, certainly know what I know and what I don't and can recall from where I know the information
> Mathematicians used to comb through model solutions because earlier systems would quietly flip an inequality or tuck in a wrong step, creating hallucinated answers.
> Brown says the updated IMO reasoning model now tends to say “I’m not sure” whenever it lacks a valid proof, which sharply cuts down on those hidden errors.
> TLDR, the model shows a clear shift away from hallucinations and toward reliable, self‑aware reasoning.
Source: https://x.com/chatgpt21/status/1950606890758476264