The Mixed Reality Lab has a long history of creating public interactive experiences in collaboration with creative practitioners. Looking across four such experiences, this keynote explores the role of code (i.e., bespoke software) in making them possible, the practicalities of non-programmers "authoring" key parts of the experience, the relationship between coding and knowledge production, and the changing nature of technical responsibilities. As well as being personally and inherently satisfying, the practical realization of novel interactive systems manifests new creative "materials", which open the door to new experiences and understandings of people and the world.CCS CONCEPTS • Human-centered computing~Human computer interaction (HCI)~Interactive systems and tools • Applied computing~Arts and humanities~Performing arts • Human-centered computing~Interaction design~Interaction design theory, concepts and paradigms