This article uses a comparative case study of two ride-hailing platforms—DiDi Chuxing in China and Uber in the United States—to explore the comparative politics of platform power in surveillance capitalism. Surveillance capitalism is an emerging economic system that translates human experiences into surveillance assets for behavioral predictions and modifications. Through this comparative study, we demonstrate how DiDi and Uber articulate their operational legitimacy for advancing their corporate interests and visions of datafication in the face of legal uncertainty. Although DiDi and Uber are both “sectoral platforms” in urban mobility with similar visions of datafication and infrastructuralization, we highlight that they deploy different discursive legitimation strategies. Our study shows that Uber adopts a “confrontational” strategy, while DiDi employs a “collaborative” strategy when they need to legitimize their data and business practices to the public and regulatory authorities. This study offers a comparative lens to examine the social and political dynamics of platform firms based in China and the United States and, therefore, contributes to understanding the various aspirational logic of platform thinking in different political contexts.