Autism is a complex neurodevelopmental disability with global prevalence of one in 100 individuals. Poor access to interventions in both under-resourced regions of high-income countries and low- and middle-income countries has deleterious effects on the health and wellbeing of individuals with autism and their families. Our objective was to utilize a reciprocal innovation framework and participatory methods to adapt and co-develop a culturally grounded group-based wellbeing and naturalistic developmental behavioural intervention (NDBI) training program for caregivers of young children with autism to be implemented in Kenya and rural Indiana. This study was conducted within the Academic Model Providing Access to Healthcare (AMPATH) program. An evidence-informed Naturalistic Developmental Behavioral Intervention (NDBI) previously utilized in Indiana was adapted and iteratively refined using the Ecological Validity Framework (EVF) by a team of US and Kenyan disability experts. Key adaptations to the program were made across the EVF domains of language, persons, metaphors/content, concepts, goals, methods, and context. Substantial cultural adaptations were made to the NDBI following the EVF model, including the addition of traditional Kenyan cultural practices, use of narrative principles, and focus on daily routines over play. Pepea, the adapted program, involves 10 group sessions covering content in basic education on autism, positive caregiver coping strategies, and behavioural skills training to promote child communication and reduce challenging behaviour. Key adaptations for Pepea were integrated back into a US NDBI caregiver training program. This study fills a critical gap by detailing the adaptation process of a caregiver wellbeing and naturalistic developmental behavioural training program for caregivers of children with autism in low-resource settings. Our next steps are to report on mixed-methods outcomes from pilot implementation. Our long-term goal is to apply these insights to advance sustainable and scalable autism intervention services across the globe.