LongR: RL with dense utility rewards boosts long-context reasoning by 9% on LongBench v2

PKU · hf · 2026-10-14

Researchers from Peking University, SJTU and Tsinghua propose LongR, a framework addressing sparse outcome rewards in long-context reasoning. It combines a dynamic 'Think-and-Read' mechanism interleaving reasoning with document consultation, plus a contextual density reward based on relative information gain—no evidence annotations needed. LongR gains over 9% on LongBench v2 with consistent improvements on RULER and InfiniteBench, works across RL algorithms (DAPO, GSPO), and includes analyses of reasoning chain length and robustness to distractors.

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