Future Art Ecosystems (FAE) is a project that was launched in 2020 by Serpentine Arts Technologies dedicated to building 21st century cultural infrastructure to support art x advanced technologies (AxAT) for the public good. Defining Public AI offers an overview of the present-day AI stack, providing key onboarding information and insights addressed to a broad range of audiences across the cultural sector and beyond. How AI is to be understood, assessed, and approached can have considerable influence over the future of regulation, governance, and ownership at each layer of the AI stack.