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Depth-Breadth Synergy in RLVR: Unlocking LLM Reasoning Gains with Adaptive Exploration
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Proposes DARS, a difficulty-adaptive multi-stage rollout sampler that allocates extra rollouts to low-accuracy RLVR prompts, combined with full-batch large-breadth training (DARS-Breadth) to jointly improve Pass@1 and Pass@K on math reasoning.
Problem
GRPO-style RLVR under-weights hard, low-accuracy problems through a cumulative-advantage bias, capping Pass@K; increasing rollout size alone does not reliably help, and the role of training batch size (breadth) for Pass@1 is unclear.
Approach
Estimate per-prompt difficulty with a cheap pre-rollout, then allocate extra rollouts to hard prompts via ET or HW schedules that re-balance cumulative advantage (and induce log-odds or max-likelihood objectives); pair this with very large batches using full-batch PPO epochs so breadth boosts Pass@1 and sustains entropy.
Key results
- DARS-7B-HW-Breadth reaches Avg@128 of 58.4 vs 55.3 for the RLVR baseline on Qwen2.5-Math-7B, and Pass@128 of 83.4 vs 81.4.
- On Llama-3.1-8B, DARS-Llama-HW-Breadth reaches Pass@128 of 68.7 vs 56.5 for the GRPO baseline.
- DARS-ET cuts average rollouts per prompt by 52.5% for Qwen2.5-Math-1.5B relative to Depth-Naive (15.2 vs 32) while reducing time per step by 35.8%.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Increase rollout size to 32 (Depth-Naive) (ablation) | Qwen2.5-Math-1.5B · Overall test (5 math benchmarks) | Pass@128: 79.6 -> 79.9 Pass@1 small; Pass@128 79.9 vs 79.6 is not reported as hurt; see Pass@128 80.3 for 7B | Hurt |
| Increase batch size to 3072 (Breadth-Naive) (ablation) | Qwen2.5-Math-1.5B · Overall test (5 math benchmarks) | Avg@128 (Pass@1): 49.6 -> 51.5 | Helped |
| Increase batch size to 3072 (Breadth-Naive) (ablation) | Qwen2.5-Math-7B · Overall test (5 math benchmarks) | Avg@128 (Pass@1): 55.3 -> 57.7 | Helped |
| Add difficulty-adaptive rollout sampling (DARS-HW) with batch 128 (ablation) | Qwen2.5-Math-1.5B · Overall test (5 math benchmarks) | Pass@128: 79.6 -> 82.1 | Helped |
| Add difficulty-adaptive rollout sampling (DARS-ET) with batch 128 (ablation) | Qwen2.5-Math-1.5B · Overall test (5 math benchmarks) | Avg@128 (Pass@1): 49.6 -> 50.0 | No clear effect |
| Add DARS-HW to large-breadth training (DARS-Breadth) (ablation) | Qwen2.5-Math-1.5B · Overall test (5 math benchmarks) | Pass@128: 79.2 (Breadth-Naive) -> 82.2 | Helped |
| Add DARS-HW to large-breadth training (DARS-Breadth) (ablation) | Qwen2.5-Math-7B · Overall test (5 math benchmarks) | Avg@128 (Pass@1): 57.7 (Breadth-Naive) -> 58.4 | Helped |
| Add DARS-HW rollout reallocation on Qwen2.5-Math-7B (batch 128) (ablation) | Qwen2.5-Math-7B · Overall test (5 math benchmarks) | Pass@128: 81.4 -> 83.5 | Helped |
| Add DARS-HW with breadth scaling on AIME24 test-time scaling | Qwen2.5-Math-7B · AIME24 maj@8 | maj@8: 27.3 -> 43.3 | Helped |
| Add DARS-HW with breadth scaling on out-of-domain HumanEval | Qwen2.5-Math-1.5B · HumanEval Avg@64 | Avg@64: 41.1 -> 49.5 | Helped |
| Use HW schedule vs ET schedule for DARS (ablation) | Qwen2.5-Math-1.5B and 7B · Overall test | Pass@128: 1.5B: 81.2 (ET) -> 82.1 (HW); 7B: 81.7 (ET) -> 83.5 (HW) | Helped |
Surprising findings
- Naively increasing rollout size can harm Pass@K for Qwen2.5-Math-1.5B.
- Naively increasing batch size to 3072 harms Pass@128 for Qwen2.5-Math-1.5B even while improving Pass@1.
Limitations
- Experiments are limited to Qwen2.5-Math and Llama-3.1-8B base models and mainly to math reasoning.
- Full-batch updates with batch size 3072 are needed for breadth gains, which increases compute per step.
- Pass@K gains can decline with prolonged training, and checkpoint selection depends on test-set metrics.
Experimental setup
Datasets: OpenR1-45K MATH train split
Benchmarks: MATH500 OlympiadBench MinervaMath AIME24 AMC23 GPQA-Diamond HumanEval
Metrics: Pass@1 (Avg@128) Pass@128 Pass@K maj@8 maj@16
Baselines: Dr. GRPO (RLVR baseline) Depth-Naive (rollout size 32) Breadth-Naive (batch size 3072) MaxRL GRPO
Builds on: GRPO Dr. GRPO PPO LUFFY
Closest papers by meaning
- Does Reinforcement Learning Really Incentivize Reasoning Capacity in LLMs Beyond the Base Model? (NeurIPS 2025 · similarity 0.92)
- Reinforcement Learning with Verifiable Rewards Implicitly Incentivizes Correct Reasoning in Base LLMs (ICLR 2026 · similarity 0.92)
- Reinforcement Learning for Reasoning in Large Language Models with One Training Example (NeurIPS 2025 · similarity 0.92)
- On the Direction of RLVR Updates for LLM Reasoning: Identification and Exploitation (ICLR 2026 · similarity 0.91)
- DeepSearch: Overcome the Bottleneck of Reinforcement Learning with Verifiable Rewards via Monte Carlo Tree Search (ICLR 2026 · similarity 0.91)
- What are Key Factors for Updates in RL for LLM Reasoning? (NeurIPS 2026 · similarity 0.91)
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