Evolving spin magnitude: Probability density functions of the spin magnitudes, χ, reconstructed from the population inference on 59 BBHs with an IFAR ≥ 1 yr from the GWTC-3 catalog, obtained with the EVOLVING GAUSSIAN (left column), BETA TO GAUSSIAN (middle column), and BETA TO BETA (right column) spin models. Each row represents a bin in source frame mass, from 10 M_⊙ up to 100 M_⊙, to highlight the spin-mass interplay.