**1. Introduction**

Artificial intelligence (AI) is one of the most disruptive technologies of our time [1]. In simple terms, AI can be defined as machines or computers that mimic cognitive functions that humans associate with the human mind, such as learning and problem solving [2]. The field of AI is vast and constantly expanding, and such characterization concerns AI beyond its current capabilities, namely artificial narrow intelligence, thereby comprehending two potential future types of AI: artificial general intelligence and artificial super intelligence [3–5].

AI is already here. AI applications are being used in areas ranging from marketing to banking and finance, from agriculture to healthcare and security, from space exploration to robotics and transport, and from chatbots to artificial creativity and manufacturing [6,7]. In recent years, AI applications

have been also started to become an integral part of the city. AIs manage the transport systems of cities in the shape of autonomous cars [8–10]. Robots run restaurants and shops where core aspects of urban life are everyday played out, and repair urban infrastructure [11,12]. Invisible intelligent platforms govern multiple urban domains ranging from traffic to safety, and from garbage collection to air quality monitoring [13,14]. We refer to this strand of AI as *urban artificial intelligences*—where AIs are embodied in urban spaces, urban infrastructures, and urban technologies, which together are turning cities into autonomous entities operating in an unsupervised manner [15].

Focusing mostly on artificial narrow intelligence and present AI technology, this viewpoint elaborates the rise of AI in cities and discusses the *sustainability of urban artificial intelligence* from the lens of*smart and sustainable cities*[16–19]—where such cities utilize digital technologies to make infrastructure services more efficient and reactive to reduce resource consumption, increase environmental quality, and cut down on carbon emissions [20]. In other words, this viewpoint investigates how AI is being utilized in urban domains, unpacking the sustainability potential and risks that AI technology poses for our cities and their citizens.

In terms of methodology, this viewpoint deploys a thorough review of the current status of AI and smart and sustainable cities literature, research, developments, trends, and applications. Following this introduction, Section 2 highlights the key challenges that humankind faces to achieve sustainability at a planetary scale. Next, Section 3 advocates smart and sustainable cities as a potential urban model to realize sustainable futures. Section 4 puts emphasis on the increasing role of AI as an emerging technology fitting the smart and sustainable city paradigm. Afterwards, Section 5 explores the idea of a possible symbiosis between AI and smart and sustainable cities, and its likely offspring—i.e., the artificially intelligent city. Section 6 discusses how urban AIs can be improved to reach more sustainable urban futures. Lastly, Section 7 concludes the viewpoint with a set of insights meant to orientate urban research, policy and development towards a sustainable adoption of AI in cities.
