It takes more than just technological convergence to integrate generative AI with urban digital twins; it requires architecture. It necessitates the meticulous assembling of systems that vary in logic, temporality, and epistemology in addition to shape and function. One uses inference, pattern synthesis, and prediction, while the other uses simulation, feedback, and representation. Data interchange alone is not enough to coordinate these systems. It requires architectural coherence—a common framework that allows them to communicate, react, and change together.