APEX is a state-of-the-art code developed and maintained by LCI for performing probabilistic seismic hazard (PSHA) and related analyses. APEX is an improved and modularized C#-based code that benefits from many years of in-house expertise in PSHA modeling and calculation. APEX can handle very complex seismic hazard logic trees through a user-friendly interface. APEX takes advantage of parallel computing, which decreases the PSHA running time substantially. APEX provides hazard fractiles and deaggregation by logic tree parameters, sensitivity analyses. APEX implements the most-recent ground motion models including NGA-West2 and NGA-East. APEX is developed and qualified under the LCI Quality Assurance (QA) program, which meets requirement of NQA-1 program. Moreover, APEX is verified by running the tests and comparing the results to the benchmark answers documented in the PEER Report 2018/03: “Probabilistic Seismic Hazard Analysis Code Verification.”