A Critical Look at Power Sampling when Test Time Sharpening LLMs

arXiv:2610.13653v1 Announce Type: cross Abstract: Reinforcement learning with verifiable rewards (RLVR) has substantially improved LLM reasoning, yet growing evidence suggests it mainly performs distribution sharpening: concentrating probability mass on reasoning paths the base model already produces. Recent work therefore seeks RLVR's gains without needing reward signals, by sampling from the power distribution pi_alpha propto pi_{ext{base}}^alpha via Markov chain Monte Carlo or sequential Monte Carlo. We show that these samplers fail to converge to pi_alpha under realistic compute budgets, and that their gains are largely recreated via simple Best-of-N with appropriate grading . This suggests they succeed by selecting high-probability sequences, not by approximating pi_alpha, raising a natural question: is the power distribution itself a worthwhile target? We test this hypothesis directly by fine-tuning the base model to match pi_alpha, sidestepping sampler convergence issues entirely. Despite approximating the target far more faithfully than existing samplers, this strategy yields gains that are noisy and specific to certain models and sampling tasks. Together, our results suggest that the value of power sampling lies not in faithfully targeting pi_alpha, but in the simpler goal of extracting sequences the base model already deems likely.

Source: arXiv cs.LG | 2026-10-12