We consider a series of legal provocations emerging from the proposed European Union AI Act 2021 (AIA) and how they open up new possibilities for HCI in the design and development of trustworthy autonomous systems. The AIA continues the by design trend seen in recent EU regulation of emerging technologies. The AIA targets AI developments that pose risks to society and citizens fundamental rights, introducing mandatory design and development requirements for high-risk AI systems (HRAIS). These requirements regulate different stages of the AI development cycle including ensuring data quality and governance strategies, mandating testing of systems, ensuring appropriate risk management, designing for human oversight, and creating technical documentation. These requirements open up new opportunities for HCI that reach beyond established concerns with the ethics and explainability of AI and situate AI development in human-centered processes and methods of design to enable compliance with regulation and foster societal trust in AI.