X-rays flux vs. W1 magnitude distributions for the training (left panel) and the blind samples: CSC2 (middle panel) and Chandra-COSMOS (right panel). The dashed line represents the galactic/extragalactic separation proposed in Salvato et al. (2018b), who already pointed out that bright nearby galaxies would be misclassified. The contours encompassing 50%, 80%, and 95% of the training sample distribution are over-plotted on all panels. While the CSC2 sample has a distribution similar to the training sample, the distribution of the Chandra-COSMOS Legacy sources is biased toward fainter values of X-rays and W1.