Adaptive Spectral Feature Forecasting for Diffusion Sampling Acceleration

TL;DR

This paper introduces Spectrum, a training-free spectral forecasting method for diffusion models that enables long-range feature reuse, significantly accelerating inference while maintaining high sample quality.

Contribution

The paper proposes a novel spectral forecasting approach using Chebyshev polynomials for diffusion features, improving long-horizon approximation and inference speed.

Findings

Achieves up to 4.79× speedup on FLUX.1

Maintains higher sample quality than baselines

Theoretically guarantees bounded long-term error

Abstract

Diffusion models have become the dominant tool for high-fidelity image and video generation, yet are critically bottlenecked by their inference speed due to the numerous iterative passes of Diffusion Transformers. To reduce the exhaustive compute, recent works resort to the feature caching and reusing scheme that skips network evaluations at selected diffusion steps by using cached features in previous steps. However, their preliminary design solely relies on local approximation, causing errors to grow rapidly with large skips and leading to degraded sample quality at high speedups. In this work, we propose spectral diffusion feature forecaster (Spectrum), a training-free approach that enables global, long-range feature reuse with tightly controlled error. In particular, we view the latent features of the denoiser as functions over time and approximate them with Chebyshev polynomials. Specifically, we fit the coefficient for each basis via ridge regression, which is then leveraged to forecast features at multiple future diffusion steps. We theoretically reveal that our approach admits more favorable long-horizon behavior and yields an error bound that does not compound with the step size. Extensive experiments on various state-of-the-art image and video diffusion models consistently verify the superiority of our approach. Notably, we achieve up to 4.79$\times$ speedup on FLUX.1 and 4.67$\times$ speedup on Wan2.1-14B, while maintaining much higher sample quality compared with the baselines.