We need to rethink how we assist designers with artificial intelligence (AI). AI should aim to cooperate, not automate, by supporting and leveraging the creativity and problem-solving capabilities of designers. The challenge for such AI is how to infer designers’ goals and then help them without being needlessly disruptive. We introduce AI-assisted design, a new framework for creating such AI, built around generative user models, which allow it to infer and adapt to designers’ goals, reasoning, and capabilities.