The CHAI COST Tool is a model that helps to estimate the financial impact of switching existing second-line (2L) patients to optimized, clinically superior regimens. Proactively switching existing 2L patients on protease inhibitors (PIs) to more optimal regimens, such as dolutegravir (DTG), has the potential to improve clinical outcomes for patients, as well as lead to significant commodity savings for national programs. Outputs from this tool can help inform national decision-making on optimizing 2L treatment through active switching to clinically superior drugs. Further transition planning and national quantifications can help to lead to a more granular cost-savings analysis. Please reach out to Jessica Fox (jfox@clintonhealthaccess.org) with any questions about this tool.