Generative Vision Interview Questions, issue 3, Jun 10, 2026
The KL Divergence Paradox
Senior AI Engineer interview at OpenAI, and the interviewer asks:
“Calculating the exact marginals for a 1,000-step diffusion trajectory is computationally impossible. Yet, the DDPM loss collapses into a simple L2 regression. What specific structural assumption saves us from infinite computational complexity?”
How calculating the exact marginals of a 1,000-step trajectory is computationally impossible, and the simple assumption that silently saves diffusion models from math that would otherwise stall train
The full answer, with the mechanism and the arithmetic, is for paid subscribers on Substack.