This paper presents a dynamic study of fuel cell gas turbine (SOFC/GT) hybrid systems, focusing on the response to a drastic transient in anode fuel composition for constant turbine speed operations. This work is motivated by the potential of fuel cells for fuel flexibility, which could extend the opportunities for sustainability and profitability in energy conversion systems. A combination of hardware and numerical models in a hybrid simulator is used to investigate the transient trajectories of fuel cell process variables as well as the consequent impacts of fuel cell thermal effluent on the integrated gas turbine engine. The conversion of thermal energy stored in the fuel cell stack to chemical energy during the reforming at the beginning of the cell resulted in a 17% increase in thermal effluent from the fuel cell to the turbine in the first few seconds of the transient. Fuel cell solid temperature gradients increased by 39% at 250 s from the initiation of the transient. The distributed dynamic performance of the fuel cell in terms of the fuel composition gradient, thermal, and electrochemical performance across the fuel cell length was carefully characterized, considering their interactions and their impacts on the total system performance. (C) 2015 Elsevier Ltd. All rights reserved.