China's ongoing transition to a modern urban-centered economy is accompanied by ambitions of sustained economic growth as well as promises of environmentally sustainable futures for its cities. In this paper we critically assess how these two ideas are combined and translated into realities on the ground by examining three low-carbon development projects in Shanghai: Anting New Town, Dongtan Eco-City, and Hongqiao CBD's low-carbon transportation hub. By mobilizing insights from the academic field of Sustainability Transitions – specifically on expectations, experimentation and innovation journeys – we show how the original plans derailed and why until now there has been limited success in living up to the promises of sustainability. To realize the promises more fully in future projects we identify three broad lessons for the actors involved: they should nurture a set of parallel pathways, foster a more experimentalist mindset, and learn to embrace uncertainty.

Currently little is known about how institutional arrangements co-evolve with urban experimentation. This paper mobilizes neo-institutional literature and recent urban experimentation literature as a framework to explore how and why institutional arrangements differ across urban contexts. Empirically the paper focusses on smart city initiatives in Amsterdam, Hamburg and Ningbo. These three cities are frontrunners in adopting a comprehensive smart city agenda, but they do so in different ways. The paper examines regulative, normative and cognitive elements of institutional arrangements, explores how they shape experimentation, and reflects on their place-based specificities. The comparative analysis suggests that the focus of, and approach to, experimentation can be understood as resting in a (possibly unique) combination of strategic agency and dynamics at multiple spatial scales.