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

Sieun Hyeon, Jaeyoung Do


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.
Anthology ID:
2026.emnlp-main.1463
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
33444–33479
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1463/
DOI:
Bibkey:
Cite (ACL):
Sieun Hyeon and Jaeyoung Do. 2026. Beyond Retraining-Free MoE Compression: A Cost-Normalized Study of Post-Compression Adjustment. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 33444–33479, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Beyond Retraining-Free MoE Compression: A Cost-Normalized Study of Post-Compression Adjustment (Hyeon & Do, EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1463.pdf