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BREAD: Branched Rollouts from Expert Anchors Bridge SFT & RL for Reasoning

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arxiv 2506.17211 v1 pith:IYEQMZRZ submitted 2025-06-20 cs.LG

BREAD: Branched Rollouts from Expert Anchors Bridge SFT & RL for Reasoning

classification cs.LG
keywords modelbreadexpertsmallreasoningtracesbranchedgrpo
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Small language models (SLMs) struggle to learn complex reasoning behaviors, especially when high-quality traces are scarce or difficult to learn from. The standard training approach combines a supervised fine-tuning (SFT) stage, often to distill capabilities of a larger model, followed by a reinforcement learning (RL)stage such as Group Relative Policy Optimization (GRPO). In this paper, we investigate the fundamental limitations of this SFT + RL paradigm and propose methods to overcome them. Under a suitable theoretical model, we demonstrate that the SFT + RL strategy can fail completely when (1) the expert's traces are too difficult for the small model to express, or (2) the small model's initialization has exponentially small likelihood of success. To address these, we introduce BREAD: a GRPO variant that unifies the SFT and RL stages via partial expert guidance and branched rollouts. When self-generated traces fail, BREAD adaptively inserts short expert prefixes/hints, allowing the small model to complete the rest of the reasoning path, and ensuring that each update includes at least one successful trace. This mechanism both densifies the reward signal and induces a natural learning curriculum. BREAD requires fewer than 40% of ground-truth traces, consistently outperforming standard GRPO while speeding up the training by about 3 times. Importantly, we demonstrate that BREAD helps the model solve problems that are otherwise unsolvable by the SFT + RL strategy, highlighting how branched rollouts and expert guidance can substantially boost SLM reasoning.

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Cited by 13 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

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    Failure-prefix conditioning unlocks learning from saturated reasoning problems by conditioning on failure prefixes, improving recovery from misleading early steps and matching gains from new medium-difficulty problems.

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  11. Don't Tell the Answer, Truly Guide the Reasoning During RL Rollouts

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    HINT boosts LLM reasoning RL by injecting teacher-generated heuristic hints only on all-failed rollouts, keeping hints out of the policy-optimization prompt, and monitoring guidance quality with a new Affinity metric.

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