YouTube can now serve video at a staggering 8K resolution. Chances are that your computer will struggle with that, at least for now.
As 9to5Google notes, at least one video — Ghost Town — is now available on YouTube at a resolution of 8K. Which means, logically enough, that YouTube now supports the standard, although in the case of this particular video, it was apparently shot on a 6K-capable camera with some post-production stitching to bring it up to full 8K resolution. Google representatives told 9to5Google that 8K has technically been supported by YouTube since 2010, but Ghost Town appears to be the first video anyone's spotted with that kind of quality tagging.
It's an interesting glimpse into the future of sorts, but the reality for almost the entire YouTube audience is that 8K is a lot of wasted resolution. Unless you're on at least a 4K-capable screen you're not going to see it. That presumes, too, that you've got a connection fast enough to handle it without significant buffering issues.