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Diffusion language models reuse their KV cache across denoising steps, so quantization has to account for that

AspireAI community · arXiv (Yan Tai, Yunan Ding, Guangzhao Li)
KV cache quantization is well understood for autoregressive models, where cached prefix states are exact under causal attention. Diffusion language models break that assumption: fast dLLM inference reuses KV states across denoising steps, but bidirectional token representations change as masked tokens are revealed, so the reused cache can already differ from full recomputation before any quantization is applied. This work studies quantization under that cache-reuse error, adapting KIVI and KVQuant to Fast-dLLM-style prefix and dual cache reuse and introducing TRACE, which reconstructs feasible reveal trajectories from prompt-answer pairs to produce calibration states, plus dLLM-KVQ, which uses those trajectories to pick per-layer K-cache entries worth keeping in high precision while applying standard low-bit value quantization. Across LLaDA and Dream on GSM8K, HumanEval, MATH and MBPP, dLLM-KVQ posts the highest average score among quantized methods in the reported 4-bit and 2-bit prefix and dual cache settings.
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