PixelMoE brought LLM-style sparse expert routing to pixel-space diffusion, and hit FID 1.47 on ImageNet-1K at 256x256
AspireAI community · arXiv
Pixel-space diffusion models skip the learned tokenizer but have historically scaled densely, coupling capacity to active compute. PixelMoE transfers standard LLM-style mixture-of-experts to pixel-space generation without diffusion-specific routing or auxiliary routing objectives, combining token-choice routing with fine-grained routed experts, a shared expert for common representations, and a bias-based load-balancing strategy. A second component, Pixel-Space Hierarchical Flow Matching, varies spatial resolution along the denoising trajectory from global structure to fine detail. At comparable active parameter counts the model consistently beats dense counterparts across scales, reaching FID 1.47 at 256x256 and 1.53 at 512x512 on class-conditional ImageNet-1K without representation alignment or perceptual losses. Code and pretrained models are released.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.