Pixar's Render Farm

That seems extremely unlikely. The Renderman software they use has no issues rendering at 4k.

The 4k streaming copy of the film has stairsteps though. Like it's been upsampled. I'm sure their software can render at 4k but they choose not to for whatever reason.

are you sure that's not just an artifact of it being streamed?

It's not really that unlikely. Most films render at 2k DCI. It's not so much that the software and hardware can't render higher, it's just diminishing gains for the increased render time.

Most 4k films till very recently actually have the digital elements at 2k DCI-ish resolutions and are upscaled. I can't speak to wether soul is rendered at 2k or 4k, but it wouldn't be surprising if it was 2k upscaled.

probably. Looking at streaming 4k is just sad, as this is just wasting money (on devices and bandwidth) for marketing having abyssmal quality at 10-20Mbit/s. With a FHD-bluray weighing in at 30-50MBit/s that's nothing to wonder about though I guess..

That's more accurate, Soul was probably rendered at 2k, as most of their movies.

If a shot doesn't look good enough when upscaled, they re-render in 4k.

Actually, they used to upscale most of the movies using Nuke, but recently, started using deep learning for that. At Siggraph 2020, they gave a talk on this topic: https://s2020.siggraph.org/presentation/?id=gensub_443&sess=...