The Gas Pixel Detector (GPD) is an instrument for measuring X-ray polarization of high-energy astrophysical sources, which is on board of Imaging X-ray Polarimetry Explorer (IXPE) operating in the nominal energy range 2–8 keV. Photons with energies above 9 keV are characterized by a low-energy tail which includes fluorescence photons ejected by the copper present in the Gas Electron Multiplier. In this work, we study the capabilities of IXPE GPDs above 8 keV with Monte Carlo simulations, showing that with a proper selection of events, they could be used with a suitable sensitivity above 8 keV. Our work provides constructive guidance for the calibration and construction of next-generation X-ray gas polarimeters such as eXTP-PFA, POLAR-2/LPD, and CATCH/Type-c microsatellites.