A new report from German website Prad.de says that sources close to monitor panel manufactures have told them that the production cost of a 27″ 4K (3840 x 2160) is lower or at least equal to that of a 27″ QHD (2560 x 1440) panel. This causes monitor manufactures to use 4K panels in QHD monitors when panel supply is low or monitor demand is high.
Now no direct sources or manufacturers were mentioned, it is very likely that some 1440p monitors with 4K panels have made their way into the hands of customers. Don’t think that you are going to get 4K resolution when using one of these monitors. The panel firmware is configured to report that the maximum capability of the display is 1440p as well as internally scale the input signal accordingly, which may result in a reduced image quality.
So to scale a 2560×1440 image to 3840×2160, the scaling factor is x1.5. So you have a single pixel in the lower resolution (1440p) getting mapped onto one and a half pixels, which will increase blurriness. This is very different from a 4K display with 1920 x 1080 input, there you have each pixel being doubled in width and height, so you do have 1:1 mapping and the image does remain sharp.
If you have one of these displays and look closely you could notice visual quality differences in text. There really should not be any noticeable difference in media playback or gaming. Below is a simulated monitor test image, with native 1440p on top and 1440p scaled to 4K on bottom.
So how do you know if you have a 1440p display with a 4K panel? One way would be to look up the pixel size specification for you display. For 1440p displays it should be around 0.23 mm, for a 4K panel it will be 0.16. So if you monitor lists that number it probably comes with a 4K panel.