Suppression Difficulty Index (SDI) is an expert-based model of how potential fire behavior and operational factors combine to influence suppression difficulty across broad landscapes (Rodríguez y Silva et al. 2020). The formulation for SDI is premised on the concept that fire behavior acts as a driving force in the numerator and conditions that facilitate suppression act as resisting forces in the denominator. The numerator, also called the energy behavior index (Ice), grows in response to conditions that increase fire behavior, so SDI will increase where and when fuel, topography, and weather conditions promote extreme fire behaviors. The denominator sums the values for sub-indices representing how accessibility (Ia), penetrability (Ip), and fireline creation (Ic) influence suppression opportunities across the landscape. Higher values for sub-indices in the denominator indicate better conditions for suppression, which lowers SDI for a given energy behavior index value in the numerator. The United States implementation of SDI includes an additional slope factor to reflect that working in steep environments is difficult regardless of the fire behavior and other operational factors. This edition of SDI was modeled using 2026 capable fuels data. The flame length and heat per unit area inputs to SDI were modeled for typical large wildfire conditions in Alaska (Fuel moistures of 1-hr: 6%, 10-hr: 7%, 100-hr: 8%, Herbaceous: 85%, Woody: 100%; Wind speeds of 15-mph @ 20-ft in the uphill direction; Finney crown fire initiation model). See the full methods report for more details.