This case study series features key findings from the 4.5-year-long Ambitious City Promises Project (ACP) that co-created climate action policies with stakeholders in Southeast Asian megacities. Three core principles guided ACP’s efforts: Inclusion, Exchange, and Action. This case study highlights the innovative potential of exchange activities, with project implementation pilot projects and eventual integration into Hanoi’s climate action policies as proof of bottom-up exchange benefits. Hanoi ultimately reoriented its existing policies towards a whole-of-society approach that emphasizes cross-cutting societal interventions and inclusivity.