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V1: Unifying Generation and Self-Verification for Parallel Reasoners
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Proposes V1, a framework pairing uncertainty-guided tournament-based pairwise self-verification at inference (V1-Infer) with an online RL method that co-trains one model as generator and pairwise self-verifier (V1-PairRL).
Problem
Parallel reasoning (sampling N solutions and selecting one) is bottlenecked by self-verification; pointwise scalar scoring of candidates by LLMs is poorly calibrated, and self-aggregation can cause diversity collapse. The paper asks how to self-verify candidates pairwise efficiently and how to train
Approach
Replace pointwise self-scoring with pairwise self-verification where the same model rates two solutions (1-10), aggregated via magnitude-weighted win rates and allocated by a two-phase Swiss-style tournament that focuses comparisons on uncertain near-tie pairs; and co-train generation and pairwise verification online within GRPO-style RL using a sparsity-thresholded verifier reward and correct-con
Key results
- V1-Infer improves Pass@1 by up to 10% over pointwise verification (e.g., GPT-OSS-20B on HMMT +10.0%, CodeContests 66.06% to 73.33%).
- V1-PairRL achieves +6.5% on LiveCodeBench-v5 over V1-PointRL at 2x budget (53.9% vs 47.4%) and +8.9% on CodeContests over RL baseline under V1-Infer.
- On SWE-bench Lite with Gemini-2.5-Flash (N=8), pairwise verification reaches 33.3% resolve rate vs 28.3% pointwise and 26.3% vanilla.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| pairwise self-verification (V1-Infer) instead of pointwise scoring | GPT-OSS-20B · CodeContests | Pass@1 after verification: +7.3% | Helped |
| pairwise self-verification (V1-Infer) instead of pointwise scoring | Qwen3-4B-Instruct · CodeContests | Pass@1 after verification: +6.7% | Helped |
| pairwise self-verification (V1-Infer) instead of pointwise scoring | GPT-OSS-20B · LiveCodeBench-v5 | Pass@1 after verification: +8.6% | Helped |
| pairwise self-verification (V1-Infer) instead of pointwise scoring | Qwen3-4B-Instruct · LiveCodeBench-v5 | Pass@1 after verification: +4.3% | Helped |
| pairwise self-verification (V1-Infer) instead of pointwise scoring | GPT-OSS-20B · HMMT | Pass@1 after verification: +10.0% | Helped |
| pairwise self-verification on SWE-bench Lite patches | Gemini 2.5 Flash · SWE-bench Lite | Resolve rate: +5.0% over pointwise, +7.0% over vanilla | Helped |
| uncertainty-guided Swiss pairing vs random pairing (ablation) | GPT-OSS-20B · LCB-v6 (budget 3x) | Accuracy: +3.8% | Helped |
| joint pairwise verification RL co-training (V1-PairRL) vs pointwise co-training (V1-PointRL) | Qwen3-4B-Instruct-2507 · LiveCodeBench-v5 (2x budget) | Pass@1 with test-time verification: +6.5% | Helped |
| joint pairwise verification RL co-training (V1-PairRL) vs standard RL baseline | Qwen3-4B-Instruct-2507 · CodeContests (base Pass@1, N=16) | Pass@1: +8.7% | Helped |
| joint pairwise verification RL co-training (V1-PairRL) vs standard RL baseline | Qwen3-4B-Instruct-2507 · LiveCodeBench-v5 (base Pass@1, N=16) | Pass@1: +2.9% | Helped |
| co-evolving (online) verifier training vs offline non-co-evolving verifier data (ablation) | Qwen3-4B-Instruct-2507 · LiveCodeBench and CodeContests (V1-Infer 2x) | Pass@1 | Helped |
| pointwise verification compared with pairwise verification in RSA-style aggregation | Qwen3-4B-Instruct / GPT-OSS-20B · LCB-v6 with RSA comparison | Pass@N across aggregation steps | Hurt |
Surprising findings
- Recursive self-aggregation shows diversity collapse: Pass@N monotonically decreases with aggregation steps, so refined Pass@1 rarely exceeds initial Pass@N.
- Without a sparsity threshold on the verifier reward, the verifier collapses to safe middle-ground scores (v=0.5) for every solution.
Limitations
- RL training is instantiated only for code generation on one model (Qwen3-4B-Instruct-2507).
- Trained model results use 3 seeds and budget exploration limited to 1x and 2x due to compute cost.
- Verifier reward requires ground-truth correctness labels from unit tests, limiting applicability to verifiable domains.
Experimental setup
Datasets: DeepCoder training set DeepCoder validation set LiveCodeBench-v5 LiveCodeBench-v6 CodeContests SWE-bench Lite AIME 2025 HMMT 2025
Benchmarks: LiveCodeBench-v5 LiveCodeBench-v6 CodeContests SWE-bench Lite AIME 2025 HMMT 2025
Metrics: Pass@1 Pass@N resolve rate accuracy vs. verification budget
Baselines: pointwise self-verification Recursive Self-Aggregation (RSA) standard RL (GRPO-style) V1-PointRL random pairwise verification vanilla first-candidate selection
Builds on: GRPO DAPO Dr. GRPO Recursive Self-Aggregation DeepCoder
Closest papers by meaning
- Variation in Verification: Understanding Verification Dynamics in Large Language Models (ICLR 2026 · similarity 0.91)
- What If We Allocate Test-Time Compute Adaptively? (ICML 2026 · similarity 0.90)
- Sample, Scrutinize and Scale: Effective Inference-Time Search by Scaling Verification (ICML 2025 · similarity 0.89)
- SCALE: Selective Resource Allocation for Overcoming Performance Bottlenecks in Mathematical Test-time Scaling (AAAI 2026 · similarity 0.89)
- Scaling Code-Assisted Chain-of-Thoughts and Instructions for Model Reasoning (NeurIPS 2025 · similarity 0.89)
- TrimR: Verifier-based Training-Free Thinking Trimming for Efficient Test-Time Scaling (ICLR 2026 · similarity 0.88)
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