Over the last decade, many urban climate change experiments have emerged to go beyond traditional role of the state in environmental governance. These activities provide a real world evidence base for how a low-carbon world could be realised and have the potential to fundamentally change the way that cities are conceived, built, and managed. Most urban climate change experiments are designed to be geographically and temporally bounded to accelerate innovation activities and realise actual changes on the ground. But what if urban experiments did not scale up? What if, instead of informing existing modes of urban governance, they became the dominant approach to governing cities? What would a ‘city of permanent experiments’ look like and how would it function? This chapter speculates on the implications of experimentation as the new mode of governance for twenty-first century cities. Here, experiments are not interpreted as one-off trials but as new modes of governance in themselves. This emerging form of urban governance is characterised by uncertainty, recursive learning processes, and spatial fragmentation with multiple unknown implications on the politics of cities in the future.