Background <p>Contingency management (CM) is the most effective treatment for stimulant use, but is underutilized due to implementation challenges. Digital CM platforms have shown promise in addressing barriers to implementation, but there is limited understanding of factors impacting delivery of a digital CM platform over time. The goal of this longitudinal study was to measure change in implementation determinants affecting uptake of a digital CM platform in opioid treatment programs (OTPs) for individuals who are stimulant users. The study used a novel assessment tool called the Inventory of Factors Affecting Successful Implementation and Sustainment (IFASIS) to compare implementation determinants across OTPs and measure changes in determinants over a 6-month implementation period.</p> Methods <p>Five OTPs in Rhode Island completed the IFASIS prior to and 6&#xa0;months into implementation of a digital CM platform. OTP staff completed the IFASIS as a team. Twenty-seven items measuring external context, internal context, intervention factors, and recipient factors were each rated on the impact of the factor on implementation (scores 1–2 = barrier, 3 = neutral, 4–5 = facilitator) and the importance of the factor (1 = not important to 3 = very important). Teams also verbalized the rationale for their ratings. Interviews were recorded and transcribed for rapid qualitative analysis. Quantitative ratings were recorded and median scores for each item were calculated.</p> Results <p>Internal organizational factors such as leadership commitment to implementation and organizational policies were perceived as becoming greater barriers to implementation over time. Staff capacity was perceived as a stable facilitator across sites despite sites experiencing turnover and new hires from baseline to follow-up. Despite initial perceptions of recipient and intervention factors as facilitators, these factors were generally viewed as neutral or as barriers at follow-up. Staff comments revealed unanticipated challenges in referring and engaging patients that contributed to the shift in their ratings.</p> Discussion <p>Findings underscore the complex and dynamic nature of implementation determinants and highlight the importance of monitoring recipient and intervention factors when implementing digital CM platforms. Results of this study suggest the need to help OTP staff set realistic expectations about the implementation process, particularly with regard to the ease of identifying and engaging patients.</p>