Over the past two decades, science diplomacy has been cast in a glow of hopeful optimism, especially by academics. It was framed as the art of bridge building, opening channels between adversaries, a common language across cultures, and a refuge for dialogue in times of political rupture. This aspirational model helped connect scientists across geopolitical divides, built trust, and was a cornerstone of post–Cold War internationalism. In recent years, these ideals have become increasingly affected by the pull of geopolitics. As multilateralism falters and geopolitical rivalries intensify, nations are putting greater emphasis on science and technology as strategic assets. For science diplomacy to remain relevant in this era, it must develop a new mode of engagement—transactional science diplomacy…