  In this paper, we present DiT-MoE, a sparse version of the diffusion
Transformer, that is scalable and competitive with dense networks while
exhibiting highly optimized inference. The DiT-MoE includes two simple designs:
shared expert routing and expert-level balance loss, thereby capturing common
knowledge and reducing redundancy among the different routed experts. When
applied to conditional image generation, a deep analysis of experts
specialization gains some interesting observations: (i) Expert selection shows
preference with spatial position and denoising time step, while insensitive
with different class-conditional information; (ii) As the MoE layers go deeper,
the selection of experts gradually shifts from specific spacial position to
dispersion and balance. (iii) Expert specialization tends to be more
concentrated at the early time step and then gradually uniform after half. We
attribute it to the diffusion process that first models the low-frequency
spatial information and then high-frequency complex information. Based on the
above guidance, a series of DiT-MoE experimentally achieves performance on par
with dense networks yet requires much less computational load during inference.
More encouragingly, we demonstrate the potential of DiT-MoE with synthesized
image data, scaling diffusion model at a 16.5B parameter that attains a new
SoTA FID-50K score of 1.80 in 512$\times$512 resolution settings. The project
page: https://github.com/feizc/DiT-MoE.
