Last But Not Least: Boundary Attention CalibratiON for Multimodal KV Cache Compression

Tianhao Chen, Yuheng Wu, Kelu Yao, Xiaogang Xu, Xiaobin Hu, Dongman Lee


Abstract
Multimodal Large Language Models (MLLMs) achieve strong vision-language reasoning but incur large KV caches and high decoding latency with long visual contexts. Existing compression methods rely on observation window attention for stable token importance estimation, yet this aggregation can dilute sparse critical evidence and discard answer-relevant tokens under aggressive compression. We identify last query attention as a complementary signal for recovering such evidence, though its irrelevant signals may introduce additional noise. We propose BACON, a plug-and-play method that calibrates observation window attention with last query evidence while suppressing noise through intra-layer coherence and inter-layer persistence. Across diverse benchmarks, models, budgets, and compression methods, BACON improves multimodal KV-cache compression by 7.5% on average under the most aggressive budget, with gains up to 30.9%.
Anthology ID:
2026.emnlp-main.331
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:
7619–7639
Language:
URL:
https://aclanthology.org/2026.emnlp-main.331/
DOI:
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Cite (ACL):
Tianhao Chen, Yuheng Wu, Kelu Yao, Xiaogang Xu, Xiaobin Hu, and Dongman Lee. 2026. Last But Not Least: Boundary Attention CalibratiON for Multimodal KV Cache Compression. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 7619–7639, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Last But Not Least: Boundary Attention CalibratiON for Multimodal KV Cache Compression (Chen et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.331.pdf