With its rapidly growing population and economy, ASEAN’s medium-term climate ambition is crucial to global mitigation efforts. While all ASEAN Member States (AMS) have communicated their medium-term ambitions through updated Nationally Determined Contributions (NDCs) submitted in 2020–2021, the region’s emissions trajectory is still not in line with a 1.5 or 2-degree scenario. However, assessing and comparing ASEAN NDCs is a complex task given the varying types of mitigation targets and actions chosen by each country. In this article, we apply an assessment framework to examine AMS’ strategies for raising mitigation ambition. Overall, AMS’ economy-wide targets need to be stronger to be Paris-aligned, but the growth in sector-scale targets shows progress in the development and mainstreaming of climate strategies. By identifying similar approaches to ambition enhancement, we placed AMS in four groups, each with different needs and recommendations for the planning of successive NDCs; thus clarifying the varying stages of progress in climate ambition among AMS. Cambodia, Laos and Myanmar set or strengthened economy-wide and sectoral targets and consolidated new mitigation actions, and can explore the expansion of target coverage in future. Brunei, Singapore and Vietnam made greater efforts to strengthen, add, or expand coverage of economy-wide GHG targets, but expert and public perceptions suggest that overall ambition gaps remain. Malaysia and the Philippines enhanced their economy wide targets but could improve clarity on sector-scale implementation. Indonesia and Thailand did not add significant updates on mitigation ambition in their NDCs compared to other national planning documents and may consider including more details in future NDCs to facilitate international support.