PROJECT SUMMARY Pediatric obesity remains a significant public health problem affecting one in six US children, yet line evidence- based pediatric obesity treatments are not widely available in real-world settings. A key barrier is the sustainability of pediatric obesity interventions, particularly after research studies conclude. To maximize the health impact of pediatric obesity interventions in diverse settings, there is a critical need to understand what factors affect sustainability. The parent grant is currently conducting a type 2 hybrid trial to develop (Aim 1) and test (Aim 2) an implementation toolkit (The “Trailguide”) for Fit Together, a pediatric-obesity intervention, at two new sites and develop a dissemination strategy (Aim 3) for a broader audience (R01HD100417). All components of the implementation toolkit are informed by the Fit Together pilot data and are consistent with current recommendations. However, existing data on pediatric obesity program sustainability is limited, and sustainability data collection at Fit Together pilot sites was disrupted by COVID-19 related program closures. The absence of program-specific data to guide effective sustainability strategies represents a clear evidence gap, and a key barrier to future dissemination. The overarching goal of the proposed supplement is to develop effective, evidence-based strategies to support sustainability of pediatric obesity interventions. Our primary objective research is to create an evidence base for effective sustainability of the Fit Together intervention, and enhance the dissemination plan (Aim 3) of the parent study. We will achieve this objective through the following specific aims: (1) Identify and describe facilitators and barriers to sustainability for the Fit Together intervention, informed by the Sustainability Framework; (2) Refine the implementation toolkit by matching sustainability barriers to strategies using the Program Sustainability Assessment Tool (PSAT) Action Items and partner listening sessions. We will use explanatory sequential mixed methods, adding additional data collection from the pilot sites to the sites included in the parent grant. We will first quantitatively identify barriers and facilitators of sustainability using data from the PSAT. These findings will guide the development of a semi- structured interview guide for program directors and coordinators (n=24). For Aim 2, we will conduct a 1.5 to 2 hour facilitated listening session with Fit Together program directors and coordinators to receive feedback on sustainability strategies for the refined implementation toolkit. The proposed work is expected to have a positive impact because it will facilitate dissemination of under-utilized recommendations for pediatric obesity treatment.