Methane- (CH₄), carbon-monoxide- (CO), and water- (WK) sensitive spectral indices for all objects in the ExoGRAVITY Spectral Library. For reference, young dwarfs (<10 Myr) and field dwarfs from the literature are shown in the background. For the ExoGRAVITY sample, objects are considered young if they have an estimated age of <50 Myr or if they are members of the Argus moving group.