Here, we elucidated the dynamic gas transport behavior in the anode porous transport layer (PTL) of polymer electrolyte membrane (PEM) electrolyzers via in operando synchrotron X-ray imaging. The imaging results showed that the gas saturation in the PTL reached steady state more rapidly with a steep current density ramp-up and a shallow ramp-down (compared to a shallow ramp-up and a steep ramp-down, respectively). Additionally, the gas accumulation was characterized by a faster response time compared to that of the gas removal due to the relatively slow migration of residual gas from the catalyst layer-PTL interface to the flow channels. Furthermore, we investigated the impact of gas response behavior on gas saturation during intermittent electrolyzer operation. Intermittent operation led to an increase in residual gas accumulation, which negatively impacted the electrolyzer performance. Our results are key for informing design and operating strategies for mitigating such hysteresis effects and improving the performance of PEM electrolyzers when coupled with intermittent renewable energy sources.