With Malaysia, Indonesia, Vietnam, and Thailand joining BRICS as partner countries, the alliance now includes 22 nations, representing 28% of the global economy and over 3 billion people. This expansion signifies a potential shift in climate action strategies, technology exchange, and green finance efforts across the developing world. However, balancing rapid economic growth with sustainability remains a challenge. For Southeast Asia, joining BRICS presents a critical opportunity for collective action on climate goals, green technology sharing, and sustainable development policies, while also introducing new pressures on natural resources and ecosystems.