The Southeast Asian region is confronted with a dual challenge, characterised by a rapid escalation in energy demand and the pressing imperative for substantial decarbonisation. Open-source energy models allow to develop transition pathways while offering transparency and collaborative potential. However, their adoption in the region remains limited due to data gaps and model accessibility. Here, we present PyPSA-ASEAN, an open-source sector-coupled energy system model designed to support Southeast Asia’s energy transition. The model features high spatial and temporal resolution. In this study we validate PyPSA-ASEAN against historical 2025 energy system data across ASEAN countries, confirming its accuracy in replicating observed system characteristics.