While the XTx43/XTx44 support rendering 4K graphics (with the Full resolution graphics option enabled), other 4K-capable models (XDx34, HDx24, etc.) render graphics at HD. When you create a 4K presentation for one of these models, the canvas will read as 1920x1080, which will then upscale to 3840x2160 when you publish the presentation.
The above process applies to graphics/HTML only: All 4K-capable models render 4K videos at their native resolution without upscaling.
For an upscaled 4K presentation, the size and position coordinates must be halved for all zones: For example, if you wish to display a second video that is HD (1920x1080) in the lower-right quadrant of the screen, you will need to set the video zone size (W:H) and position (X:Y) to 960x540.
Note: HTML pages in an upscaled 4K presentation must have a specified width and height (up to 1920x1080).