Yes, it will. OS_get_window_size() on the other hand returns the size of your window (so it will change depending on if you are in fullscreen mode or window mode and which size the actual window is
But be aware that this value changes depending is HighDPI is active or not. For example with my Mac screen without HighDPI it returns 1680x1050 but with HighDPI on it returns 3360x2100
(I would recommend you activate it, you would avoid the headache of having low-quality graphics on those types of monitors)