I'd guess a 4d version of: https://paperswithcode.com/method/nerf

This might be what you’re looking for: https://gafniguy.github.io/4D-Facial-Avatars/

I guess this means dimensionality reduction for example with the use of a convolutional autoencoder.

Unity recently acquired Ziva, which specializes in the detailed animation of humans and other animals. They were known for their (not realtime) physics-based solutions, but now they have an ML model for faces, apparently. As far as I know, it's still in beta and not widely available. Unity says they will re-release this demo with the Ziva face in a matter of weeks and the quality will be even higher. And possibly allowing interactivity as well?? I guess we'll see in a few weeks.

Superresolution. You have a lower resolution animation (less pixels = less calculations) and then use superresolution to turn that into a 4K image. This is reality right now for NVIDIA GPUs ( I think it’s called DMSS)

They are talking about compressed geometry, not pixels. This is more similar to alembic and other geometry streaming tech https://en.wikipedia.org/wiki/Alembic_(computer_graphics)

There is one out there from 5 years ago or so that is similar to Google's Seurat but for animated stuff, I think pre-baking triangle culling for different views within a limited volume. I can't remember the name of it, from the details I remember (there was a realistic orangutan or something like that rendered with fur) I should be able to find it on Google, but Google search has become degraded recently.

Nvidia DLSS is an important part of how they achieved 30Hz at 4k resolution, but that's more of a shading assist and doesn't affect the animation. The facial animation will be compressed with Ziva's ML solution.

aka "enhance": https://www.youtube.com/watch?v=Vxq9yj2pVWk