Power-SMC: Low-Latency Sequence-Level Power Sampling for Training-Free LLM Reasoning

Seyedarmin Azizi; Erfan Baghaei Potraghloo; Minoo Ahmadi; Souvik Kundu; Massoud Pedram

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arXiv · 2602.10273

Power-SMC: Low-Latency Sequence-Level Power Sampling for Training-Free LLM Reasoning

Seyedarmin Azizi·Erfan Baghaei Potraghloo·Minoo Ahmadi·Souvik Kundu·Massoud Pedram

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Abstract

Many recent reasoning gains in large language models can be explained as distribution sharpening: biasing generation toward high-likelihood trajectories already supported by the pretrained model, rather than modifying its weights. A natural formalization is the sequence-level power distribution $π_α(y\mid x)\propto p_θ(y\mid x)^α$ ($α>1$), which concentrates mass on whole sequences instead of adjusting token-level temperature. Prior work shows that Metropolis--Hastings (MH) sampling from this distribution recovers strong reasoning performance, but at order-of-magnitude inference slowdowns. We introduce Power-SMC, a training-free Sequential Monte Carlo scheme that targets the same objective while remaining close to standard decoding latency. Power-SMC advances a small particle set in parallel, corrects importance weights token-by-token, and resamples when necessary, all within a single GPU-friendly batched decode. We prove that temperature $τ=1/α$ is the unique prefix-only proposal minimizing incremental weight variance, interpret residual instability via prefix-conditioned Rényi entropies, and introduce an exponent-bridging schedule that improves particle stability without altering the target. On MATH500, Power-SMC matches or exceeds MH power sampling while reducing latency from $16$--$28\times$ to $1.4$--$3.3\times$ over baseline decoding. The code is available at https://github.com/ArminAzizi98/Power-SMC.

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Seyedarmin Azizi, Erfan Baghaei Potraghloo, Minoo Ahmadi, Souvik Kundu, Massoud Pedram. 2026-03-23. Power-SMC: Low-Latency Sequence-Level Power Sampling for Training-Free LLM Reasoning. https://arxiv.org/abs/2602.10273

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