We present an analysis of ultra-high energy cosmic ray (UHECR) mass composition based on four years of data collected by Telescope Array’s expansion project, TAx4. Reconstructing events in hybrid mode, combining information from both the fluorescence detectors (FDs) and surface detectors (SDs), we measure the mass composition of UHECRs using the distribution of the depth of air shower maxima (Xmax). The hybrid technique enhances the precision of the reconstructed shower geometry, leading to more accurate Xmax measurements. Our results suggest a predominantly light composition, with protons and light nuclei comprising the majority of cosmic rays above 10^18.5 eV.