Greedy Multi-Path Block Verification for Faster Decoding in Speculative Sampling

• URL: http://arxiv.org/abs/2602.16961v1
• Date: Wed, 18 Feb 2026 23:55:01 GMT
• Title: Greedy Multi-Path Block Verification for Faster Decoding in Speculative Sampling
• Authors: Rahul Thomas, Arka Pal,
• Abstract summary: We show that block verification is optimal even over verification algorithms that use off-path probabilities.<n>We formulate an efficient method called greedy multi-path block verification (GBV)<n>On Llama-3 70B, GBV can improve the end-to-end decoding throughput over SOTA multi-path verification methods by more than 15%.
• Score: 0.776402435567685
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: The goal of $L$-step speculative decoding is to accelerate autoregressive decoding of a target model by using a cheaper draft model to generate a candidate path of $L$ tokens. Based on a verification algorithm involving target and draft model probabilities, a prefix of the candidate sequence is accepted, and an additional correction token is sampled from a residual distribution to ensure that the final output adheres to the target distribution. While standard speculative decoding uses a verification algorithm which is independent at each token on the path, a recent extension called block verification uses a joint condition involving all sampled on-path probabilities. Block verification (BV) was shown to be optimal over all verification algorithms which use only on-path probabilities, improving on standard speculative decoding. In this work, we first show that block verification is optimal even over verification algorithms that use off-path probabilities, by constructing an information-agnostic linear program (LP). Further, we can extend our LP to the setting where the draft model samples multiple candidate paths, and use it to construct a natural class of multi-path block verification generalizations. While computing the optimal algorithm in this class is not tractable, by considering a stricter class of greedy algorithms, we can formulate an efficient method called greedy multi-path block verification (GBV). Empirically, GBV can improve block efficiency by over 30% and reduce decoding walltimes by over 15% relative to BV. On Llama-3 70B, GBV can improve the end-to-end decoding throughput over SOTA multi-path verification methods by more than 15%.

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