KV Cache Quantization for Diffusion Language Models

Yan Tai, Yunan Ding, Guangzhao Li, Siqi Luo, Chaoyang Zhang, Guangtao Zhai, Guodong Guo, Xiaohong Liu


Abstract
KV cache quantization is well studied for autoregressive language models, where cached prefix states are exact under causal attention and quantization is mainly a cache reconstruction problem. Diffusion language models (dLLMs) break this assumption. Fast dLLM inference reuses KV states across denoising steps, but bidirectional token representations can change as masked tokens are revealed, so the reused cache may already differ from full recomputation before quantization is applied. We study KV cache quantization under this cache-reuse error. We adapt KIVI and KVQuant to Fast-dLLM-style prefix and dual cache reuse, and introduce TraceKV and KProtect. TraceKV reconstructs feasible dLLM reveal trajectories from prompt-answer pairs, providing calibration states that match iterative masked decoding. KProtect uses these trajectories to choose per-layer K-cache entries that remain in high precision according to output- and attention-level behavior metrics, while applying standard low-bit value quantization. Across LLaDA and Dream evaluations on GSM8K, HumanEval, MATH, and MBPP, KProtect achieves the highest average score among quantized methods across the reported 4-bit and 2-bit prefix/dual cache settings.
Anthology ID:
2026.findings-emnlp.799
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
16937–16951
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.799/
DOI:
Bibkey:
Cite (ACL):
Yan Tai, Yunan Ding, Guangzhao Li, Siqi Luo, Chaoyang Zhang, Guangtao Zhai, Guodong Guo, and Xiaohong Liu. 2026. KV Cache Quantization for Diffusion Language Models. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 16937–16951, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
KV Cache Quantization for Diffusion Language Models (Tai et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.799.pdf