QTEA: Ternary LLMs with Sparse Residual Salient Weight and By-Column Optimization

Yipin Guo, Jie Fu, Arun M George, Tareq Mahmoud, Siddharth Joshi


Abstract
Weight-only post-training quantization (PTQ) can alleviate the computational burden of serving large language models (LLMs) at scale. However, existing PTQ methods often fail to generalize across models and suffer severe accuracy loss below 2 bits. Many leverage unstructured sparsity to mitigate this loss, but at the cost of regularity and GPU-friendly execution. We present QTEA, a sub-2-bit PTQ framework that quantizes weights into ternary values and uses salient weights as residual error compensators. To maintain hardware efficiency, residuals are assigned to selected columns with semi-structured 1:4 sparsity within the salient columns. We further add column-wise rescale refinement to GPTQ-style column-by-column quantization, alternately updating per-column scales and ternary assignments to reduce reconstruction error. We also identify order-dependent error propagation in GPTQ and introduce error decay to attenuate late-stage error accumulation. On Qwen3-14B, QTEA compresses all weights to an effective 1.7 bits per weight while improving average accuracy over the strongest ternary PTQ baseline by 16.7%. It also achieves 1.40× and 2.61× lower perplexity on WikiText and C4 respectively. This trend holds on Llama3-8B, where QTEA obtains a 6.6% accuracy gain and 1.34×/1.95× lower perplexity on the same datasets. Finally, we develop a lookup-table based kernel that achieves 7.2× faster per-token generation over an FP16 baseline.
Anthology ID:
2026.emnlp-main.1775
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
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Pages:
40441–40453
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URL:
https://aclanthology.org/2026.emnlp-main.1775/
DOI:
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Cite (ACL):
Yipin Guo, Jie Fu, Arun M George, Tareq Mahmoud, and Siddharth Joshi. 2026. QTEA: Ternary LLMs with Sparse Residual Salient Weight and By-Column Optimization. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 40441–40453, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
QTEA: Ternary LLMs with Sparse Residual Salient Weight and By-Column Optimization (Guo et al., EMNLP 2026)
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https://aclanthology.org/2026.emnlp-main.1775.pdf