YouTube rolls out 4K support to Android phones with any screen resolution
Android phones with 1080p and 720p displays can view videos in 4K resolution.
This feature is being widely implemented as per two Reddit threads (via 9to5Google). Until now, YouTube has allowed the transmission of content in the same resolution as the phone screen. This depends on the availability of 4K (2160p) content on YouTube.
It also doesn't change the actual resolution of the phone screen. For example, watching 4K content on the phone with 1080p resolution will still have the same resolution but with sharper graphics. Therefore, it is still a useful option for users who want to see better quality content.
4K is the highest resolution YouTube offers. Most flagship phones already support 1440p resolution, and the most common resolution is 1080p.
It's also worth noting that watching 4K content would require a good internet connection. YouTube is very well optimized for a poor internet connection, but a higher resolution would mean faster internet.
Reddit users have shared that they suddenly see the option to watch 4K content. It even appears on phones with 720p (HD) screen resolution. Some even suspect that it is a bug, but it seems that it is indeed a feature.
If you have a phone with a Full HD or lower resolution display, you can check if you received this feature on YouTube. Tap on the gear icon below and select the quality to see the list of available resolutions. You can select 2160p (if available) to view that video in 4K.