Apple's NTM: exact-likelihood few-step diffusion via conditional normalizing flows

Apple ML Research · rss · 2026-10-08

Apple ML Research published Normalizing Trajectory Models (NTM). Diffusion models assume sampling decomposes into many small Gaussian denoising steps — an assumption that breaks when generation is compressed to a few coarse transitions. Existing few-step methods rely on distillation, consistency training, or adversarial objectives, sacrificing the likelihood framework. NTM instead models each reverse step as an expressive conditional normalizing flow with exact likelihood training, combining shallow invertible blocks within each step and deep parallel structure across steps.

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