a)F_X/F_opt diagram for the XXL-1000-AGN. The majority of the objects classified as quasi-stellar object (QSO)/AGN (red and orange dots) fall between the log (F_X/F_opt) = ± 1 lines, while passive objects (dark blue) and stars are gathered in the bottom left corner of the plot. b) X-ray luminosity per class. QSO classified objects have the highest 2−10 keV luminosity. The colour-coding indicates the photo-z class assigned by the Random Forest in both plots: QSO − red, AGN − orange, starburst − green, star forming − blue, passive − black.