Quantizing Masked Diffusion Language Models: Storage-Quality Trade-offs and Runtime Diagnostics

Pawan Kumar, Neel Mishra


Abstract
Masked diffusion language models reuse one denoiser across many steps, so post-training quantization (PTQ) must balance predictive quality, serialized storage, and runtime memory. We evaluate LLaDA-8B-Instruct and run transfer checks on Dream-7B, MDLM-OWT, encoder-only masked LMs, LLaDA-MoE, and LLaDA2.0-mini. The 24-text calibration set is distinct from the main n=500-example-per-task evaluation. Three findings emerge. First, AWQ-4 is the closest tested 4-bit quality point at the evaluated 1.1–2.3 percentage-point resolution, although ARC-Challenge shows a detectable loss. TurboLDM-(3+1) instead provides the smallest serialized checkpoint (4.82 GiB, 3.55 effective bits) while losing quality, making it a storage-compression and diagnostic result, not a live-memory result. NF4 alone reduces peak VRAM from roughly 15 GiB to 6 GiB in our tested PyTorch/bitsandbytes runtime; this is a runtime-specific outcome, not an inherent format advantage. Second, individual attention projections are inexpensive to quantize, whereas jointly quantizing the attention block is damaging. Third, more denoising steps partly recover GSM8K loss but not multiple-choice accuracy.
Anthology ID:
2026.emnlp-industry.241
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing: Industry Track
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Pepa Atanasova, Gholamreza Haffari, Minghan Wang
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
4067–4089
Language:
URL:
https://aclanthology.org/2026.emnlp-industry.241/
DOI:
Bibkey:
Cite (ACL):
Pawan Kumar and Neel Mishra. 2026. Quantizing Masked Diffusion Language Models: Storage-Quality Trade-offs and Runtime Diagnostics. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing: Industry Track, pages 4067–4089, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Quantizing Masked Diffusion Language Models: Storage-Quality Trade-offs and Runtime Diagnostics (Kumar & Mishra, EMNLP 2026)
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https://aclanthology.org/2026.emnlp-industry.241.pdf