After recently adding support for 5K resolution, YouTube will now let you watch videos uploaded in 8K resolution natively. That’s 7680 x 4320 pixels at 30fps.
Currently there’s just one video that supports this resolution, and that too is mostly shot using two RED Epic Dragon in 6K in portrait orientation and then stitched together in Adobe After Effects to form the final 8K video. Some of the scenes are shot at 6K in landscape and then upscaled and sharpened for the higher resolution.
Playing the 8K video will require a lot of horsepower on your computer. Even with a Core i5-3570 and NVIDIA GTX 560 Ti the video was fairly choppy and dropping frames for me in Chrome, although it does seem easier to run than the 4K 60fps videos that were announced previously.
Currently, there are only a handful of cameras that can natively shoot in 8K, such as the RED Weapon Dragon, and even that can only shoot 6K for now with 8K upgrade coming later this year.