Google recently introduced the option to select the resolution of the video you are watching in the Android version of the YouTube app. Depending upon the device you are using, the maximum resolution option would differ, although it is known to get confused at times.
So far, the maximum resolution option available in the app was 1080p, even if you have happen to have a smartphone or tablet with higher resolution. But to address that minor inconvenience, the app now goes up to 1440p on select devices.
If you happen to have an Android device with higher than 1080p resolution display, you might see the 1440p resolution option in the settings while watching the video. This is, of course, assuming the video itself supports resolutions above 1080p. But like I said, the app gets confused sometimes, just like how it shows 720p as the maximum resolution for me on a Nexus 5, so if you don’t see 1440p, don’t worry. It will either arrive later or just watch it at 1080p because it looks more or less the same.