High-fidelity deterministic steady-state simulations of the Empire microreactor problem were conducted using the discontinuous finite element method–based discrete ordinate solver in Griffin, accompanied by the online cross-section self-shielding application programming interface (SSAPI). The 68-group cross-section libraries for SSAPI were generated through a series of Python scripts and using a combination of Serpent2, NJOY, and MC2-3 with ENDF/B-VII.0, VII.1, and VIII.0 data. Additionally, the 27-group libraries were generated as well to improve computational performance while maintaining the solution accuracy. The capabilities of Griffin with these three ENDF/B cross-section libraries were rigorously tested across various Empire microreactor benchmark problems, including fuel assembly and two- and three-dimensional cores with control drums rotated in or out. The calculation results convincingly demonstrated that Griffin with the cross-section libraries and SSAPI achieves accurate simulations of the Empire microreactor cores, exhibiting accuracy in terms of eigenvalue, control drum reactivity worth, and pin power distribution when compared to corresponding Serpent2 solutions.