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arXiv · 2609.06076

Beyond Retraining-Free MoE Compression: A Cost-Normalized Study of Post-Compression Adjustment

Sieun Hyeon·Jaeyoung Do
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Abstract

Retraining-free MoE compression reduces deployment memory by pruning or merging experts, but often treats the compressed checkpoint as the final artifact. We argue that this view is incomplete: compressed MoE checkpoints are better understood as compressed initializations that benefit from a tiny post-compression adjustment stage. Across two MoE LLM backbones, four pruning/merging methods, three expert-retention ratios, and 28 benchmarks, we compare LM fine-tuning and teacher-based KD under matched small-data budgets and measured GPU costs. Using only 3,000 C4 examples and a single epoch of adjustment, Full FT recovers 37.3% of the original-to-compressed performance gap on average. Moreover, LM fine-tuning is more cost-effective than standard token-level KD, and full-parameter adjustment gives the strongest cost--recovery trade-off among the tested scopes. These results suggest that retraining-free compression should be paired with small post-compression adjustment to recover a substantial portion of the performance lost during compression.

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Sieun Hyeon, Jaeyoung Do. 2026-09-05. Beyond Retraining-Free MoE Compression: A Cost-Normalized Study of Post-Compression Adjustment. https://arxiv.org/abs/2609.06076

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