log(f H α ), J_AB distribution of the reliability class predictions for unlabeled simulated galaxy spectra for Euclid. The number of faint objects predicted in C1/C2 increases when the noise component in the data is important (S1 → S2). The increased sky background injects a strong noise component of the spectra that annihilates the confidence in a measured redshift, resulting in multimodal zPDFs with high dispersion (C1/C2). In contrast, extremely bright objects with an identifiable Hα line are located in C4∕C5, because the redshift estimation is deemed very reliable when distinct spectral features are found.