The rubin_sim.skybrightness module generates predicted skybrightness values (in either magnitudes per square arcsecond for any LSST bandpass or as a SED over the relevant wavelengths). It uses the ESO skybrightness model components (includes upper and lower atmosphere emission lines, airglow continuum, zodiacal light and scattered lunar light) and has additional twilight components. The model predictions have been tested against skybrightness measurements at the LSST site.
More details about the rubin_sim version of the model and its validation for Rubin is available in An optical to IR sky brightness model for the LSST by Yoachim et. al..