Activation Residual Hessian Quantization for Low-Bit Large Language Model Inference

YiFeng Wang, Zhun Sun, Hakaze Cho, Linlin Wang, Keisuke Sakaguchi


Abstract
Low-bit activation-weight quantization is crucial for efficient large language model inference but remains fragile because activation quantization errors propagate across Transformer layers. We propose Activation Residual Hessian Quantization (ARHQ), a post-training residual-aware low-rank correction framework that directly targets this propagation. ARHQ measures the residuals produced by the deployed activation quantizer, builds an input-side residual Hessian, and identifies the weight directions that most amplify these residuals. This yields a closed-form truncated-SVD solution: residual-sensitive components are placed in a high-precision low-rank branch, while the remaining weights stay in the low-bit path. ARHQ requires no backpropagation, supports LoRA-style deployment, and complements activation smoothing. Across LLaMA-family models and Qwen3-4B-Thinking, ARHQ improves W4A4 reconstruction, reduces WikiText2 perplexity over matched-rank SVDQuant, preserves downstream reasoning and coding accuracy, and achieves up to 3.21× prefill speedup over BF16 (3.11× over AWQ W4A16) with over 60% memory saving.
Anthology ID:
2026.findings-aacl.134
Volume:
Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venue:
Findings
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
2613–2627
Language:
URL:
https://aclanthology.org/2026.findings-aacl.134/
DOI:
Bibkey:
Cite (ACL):
YiFeng Wang, Zhun Sun, Hakaze Cho, Linlin Wang, and Keisuke Sakaguchi. 2026. Activation Residual Hessian Quantization for Low-Bit Large Language Model Inference. In Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026, pages 2613–2627, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Activation Residual Hessian Quantization for Low-Bit Large Language Model Inference (Wang et al., Findings 2026)
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https://aclanthology.org/2026.findings-aacl.134.pdf