10 MWe sCO2 turbine was developed and tested for the Supercritical Transformational Electric Power (STEP) demo pilot plant, which is a supercritical carbon dioxide (sCO2) test facility located at Southwest Research Institute (SwRI) in San Antonio. The plant was assembled and commissioned for simple cycle operation, and the initial testing of the turbine was performed, including electric power generation. The project was developed in partnership between Southwest Research Institute, GTI Energy, and GE Vernova Advanced Research and is sponsored by the U.S. Department of Energy (DOE) as part of the $169 million STEP Demo project. The goal of the program is to demonstrate mechanical qualification and cycle efficiency in both the simple and recompression recuperated Brayton cycle. Initial testing in the simple cycle configuration was performed with turbine inlet temperatures up to 500°C. This talk provides mechanical and performance test results for the turbine, which provided over 8 MW of gross shaft power. Synchronization to the grid permitted almost 4 MWe of net electric power output of the plant, achieving the goals for the simple cycle configuration. Other mechanical test data will be presented, including radial vibration and bearing temperatures, along with the operating conditions of the test loop. The plant is undergoing reconfiguration into the RCBC configuration by adding a second (bypass) compressor and a second recuperator with the goal of achieving 10 MWe net electric power output and plant thermal efficiency approaching 50%.