BlockBatch: Multi-Scale Consensus Decoding for Efficient Diffusion Language Model Inference

Xiaoyou Wu, Cheng-Jhih Shih, Binfei Ji, Yong Liu, Yingyan Celine Lin


Abstract
Diffusion language models (dLLMs) generate text by iteratively denoising multiple token positions in parallel, offering an attractive alternative to strictly autoregressive decoding. In practice, however, block-wise dLLM inference exposes a difficult granularity trade-off: small blocks preserve local conditioning but require many denoising steps, whereas large blocks expose more parallelism but can make premature commitments. Existing block-wise acceleration methods either use a fixed block size or adapt block boundaries along a single decoding trajectory, leaving the complementarity among concurrently executed block-size trajectories unused. We show that block-size diversity provides a useful branching dimension. Different block sizes induce related but non-identical KV-cache trajectories: branches often share an initial prefix, bifurcate at semantically decisive positions, and later agree on syntactically lightweight tokens. Motivated by this structure, we propose BlockBatch, a training-free online inference framework that executes multiple block-size branches for the same request inside a batched forward pass. BlockBatch coordinates these branches through confidence-gated token merging, leader-based synchronization, and periodic full-sequence refreshes that re-anchor local block updates to a globally consistent KV state. Across three representative dLLMs and four datasets, BlockBatch reduces denoising NFEs by 26.6% on average and achieves a 1.33× average end-to-end speedup, with comparable average accuracy.
Anthology ID:
2026.findings-emnlp.1492
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
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SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
31747–31774
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URL:
https://aclanthology.org/2026.findings-emnlp.1492/
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Cite (ACL):
Xiaoyou Wu, Cheng-Jhih Shih, Binfei Ji, Yong Liu, and Yingyan Celine Lin. 2026. BlockBatch: Multi-Scale Consensus Decoding for Efficient Diffusion Language Model Inference. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 31747–31774, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
BlockBatch: Multi-Scale Consensus Decoding for Efficient Diffusion Language Model Inference (Wu et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.1492.pdf