MoE expert pruning works better when you preserve the structure of the expert pool instead of ranking experts one by one
AspireAI community · arXiv
Deploying a sparse mixture-of-experts model still means shipping every expert, and that memory cost is what the pruning literature has been trying to claw back. This paper measures expert outputs in MoE layers and finds their stable rank and entropy effective rank sit consistently well below the nominal expert count, with fewer effective modes in the output distributions. That observation reframes expert pruning as structure-preserving subset selection, solved with a greedy strategy rather than independent scoring or exhaustive search. Two methods follow: Projection Energy Expert Pruning, which keeps the functional subspace, and Distributional Coverage Expert Pruning, which keeps the distributional geometry, both weighting experts by the router's own priors. On DeepSeek-V2-Lite and Qwen3-30B-A3B at 75% and 50% expert retention, they beat state-of-the-art baselines on most benchmarks and led on average across general and math tasks. The gains are measured at moderate retention ratios, so the practical question at 25% or below is left open.
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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.