Adaptive Dual Reasoner: Large Reasoning Models Can Think Efficiently by Hybrid Reasoning

YuJian Zhang, Keyu Chen, Zhifeng Shen, Ruizhi Qiao, Xing Sun

Keywords: Large Language Model, Large Reasoning Model, Efficient Reasoning, Hybrid Thinking

TL;DR: We propose ADR, an adaptive dual reasoner that dynamically switches between fast and slow thinking via supervised pretraining and entropy-guided RL, achieving up to 6.1% accuracy gain with 49.5–59.3% shorter reasoning.

Abstract: Although Long Reasoning Models (LRMs) have achieved superior performance on various reasoning scenarios, they often suffer from increased computational costs and inference latency caused by overthinking. To address these limitations, we propose Adaptive Dual Reasoner, which supports two reasoning modes: fast thinking and slow thinking. ADR dynamically alternates between these modes based on the contextual complexity during reasoning. ADR is trained in two stages: (1) A cold-start stage using supervised fine-tuning (SFT) to equip the model with the ability to integrate both fast and slow reasoning modes, in which we construct a hybrid reasoning dataset through a dedicated pipeline to provide large-scale supervision. (2) A reinforcement learning stage for optimizing reasoning effort, where we introduce Entropy-guided Hybrid Policy Optimization EHPO, an RL training framework employing an entropy-guided dynamic rollout strategy for branching at high-entropy units and a difficulty-aware penalty to balance fast and slow reasoning. Across challenging mathematical reasoning benchmarks, ADR achieves an effective balance between reasoning performance and efficiency among state-of-the-art approaches. Specifically, ADR yields a performance gain of up to 6.1%, while reducing the reasoning output length by 49.5% to 59.3%.

Submission Number: 72