Meeting a federal 100% Clean Energy Standard (CES) will require and drive transformative change in the electric power sector, but the extent to which this change may occur can depend on the specific provisions included (or excluded) in a CES, and ultimately implemented. This presentation describes analysis using EPRI’s in-house energy system modeling framework, the U.S. Regional Economy, Greenhouse Gas, and Energy Model (US-REGEN), to quantify differences between approaches to implementing a federal 100% Clean Energy Standard by examining (1) changes in modeled generation portfolio choices; (2) other policy compliance choices such as electricity and credit trade and alternative compliance payments; (3) CO2 emissions; and (4) electricity prices across a range of policy design scenarios.