The present work focuses on the study of a metallic supported Pd–Ag membrane for high temperature applications with a particular attention to long-term stability. In this work, a metallic supported thin-film Pd–Ag membrane has been tested for more than 800 h and sustained hydrogen perm-selectivities higher than 200000 have been measured. Furthermore, it has been demonstrated that there is no interaction of the membrane with the Ni/CaAl2O4 reforming catalyst particles, thus resulting in a constant permeance in the fluidized bed membrane reactor mode. The membrane has been tested under steam and autothermal reforming of methane conditions and the membrane performance has been quantified in terms of the hydrogen recovery and separation factors demonstrating a good reactor performance accomplishing an enhancement in the process efficiency by in-situ selective H2 separation. A decrease in ideal perm-selectivity has been observed at high temperatures (600 °C). Small defects at the Pd/Ag surface as a result of interaction of the Pd/Ag later with the metallic support have been observed in after test membrane characterization, which provides appreciated information for the improvement in the performance and production of future membranes.