Background: The COVID-19 pandemic rapidly changed how substance use disorder (SUD) treatment services are delivered. In this qualitative study, we examined what changes SUD treatment programs in Arkansas implemented in response to the pandemic, what factors influenced their ability to implement these changes, and their reflections, outlook, and future recommendations. Methods: Between May and August 2020, we conducted semi-structured phone interviews with 29 leaders at 21 SUD programs throughout Arkansas. Interview questions focused on what changes programs implemented in response to the pandemic, barriers and facilitators to implementation, and future outlook. Interviews were thematically analyzed. Results: Programs implemented similar infection control practices, including COVID-19 screening at entry, masks, hand hygiene, and social distancing. Residential programs discontinued outside visitations and capped admissions, and outpatient programs implemented telehealth services. Clients generally responded well to the changes, however many experienced difficulties (e.g., anxiety, lack of access to telehealth). While programs welcomed additional financial support (e.g., CARES act) and looser regulatory restrictions (e.g., telehealth use), many struggled economically due to lower demand and insufficient reimbursement. Programs varied in leadership and staff responses to the pandemic, and in their capacity to implement the changes (e.g., facilities, staffing). Finally, interviewees acknowledged they were unprepared for the pandemic and were uncertain about the future. Conclusions: The insights from the COVID-19 pandemic and SUD programs' responses helps researchers, policymakers and practitioners understand what has happened during the pandemic, how to prepare for future crises, and how to build more resilient SUD and public health systems.