Same places as usual: Academia and open source foundations.
That's where 99% of all advancements in AI come from. You don't actually think Big AI is paying as many people to do computer science and mathematics research as all the universities in the world (with computer science programs)?
It's the same shit as always: Big companies commercialize advancements and discoveries made by scientist and researchers from academia (mostly) and give almost nothing back.
Big AI has partnerships with tons of schools and if it weren't for that, they wouldn't be advancing the technology as fast as they are. In fact, the only reason why many of these discoveries are made public at all is because of the agreements with the schools that require the discoveries/papers be published (so their school, professors, researchers, and students can get credit).
Like I was saying before: You don't need a trillion dollars in data centers to do this stuff. Almost all the GPUs and special chips being used (and preordered, sigh) by Big AI are being used to serve their customers (at great expense). Not for training.
Training used to be expensive but so many advancements have been made this is no longer the case. Instead, most of the resources being used in "AI data centers" (and research) is all about making inference more efficient. That's the step that comes after you give an AI a prompt.
Training a super modern AI model can be done with a university's data center or a few hundred thousand to a few million dollars of rented GPUs/compute. It doesn't even take that long!
Generative AI improves at a ridiculously fast rate. In nearly all the ways you could think of: Training, inference (e.g. figuring out user intent), knowledge, understanding, and weirder, fluffier stuff like "creativity" (the benchmarks of which are dubious, BTW).