It might be interesting to look at KL divergence or weight changes between randomly-initialized models versus base models, and between base models versus RLVR? I can’t immediately find literature on that.
A colleague (Ekdeep Singh) sent me:
There’s quite a bit of work on this: I did a couple of papers in synthetic scenarios (formal languages or synthetic data from LLMs) to see how base + SFT versus learn the data from scratch differ. My friend Andrew extended the analysis for DPO and RLVR. Old BERT era had papers like this, claiming updates are very sparse during SFT; similar work has been done for RLVR in the modern era now (also see this one for token level change analysis). High level, not much changes in a model via post-training methods, and on pretraining data the model has low KL w.r.t. base model.
Insofar as that last sentence is true, I think it’d be true mostly because it provides cover (to oneself and others) for other motivations like working on cool problems with smart people at high profile companies and getting large compensation.