Innovative models for delivering HIV and HCV care, HIV prevention (PrEP), and OUD medication at SSPs can expand PWID treatment access, uptake and engagement, but they are not well described or evaluated systematically. Building on our previous quantitative, qualitative, and economic studies of expanding HIV and HCV testing in substance use treatment programs, we propose to describe care models that provide varying combinations of HIV, HCV, and OUD medical services on-site and off-site in the fast-growing SSP sector, and evaluate the feasibility of sustainably implementing them in different geographic settings from the perspectives of the programs and their clients.