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Primal Generation, Dual Judgment: Self-Training from Test-Time Scaling
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Proposes DuST, self-training code models with GRPO to rank their own execution-labeled candidates (never rewarding generation directly), which also improves single-sample code generation and best-of-4 test-time scaling.
Problem
Code generation RL uses sparse pass/fail feedback per sample, and the comparative information revealed by generate-then-judge test-time scaling is discarded after inference without improving the generator.
Approach
Train the same model on-policy via GRPO to rank its own execution-labeled mixed-correctness candidate groups with a pairwise correct-over-incorrect ranking reward; the discriminative judgment training transfers back to improve primal code generation, unlike SFT on the same ranking data.
Key results
- Qwen3-30B-Thinking on LCB v6: test-time scaling accuracy 68.7% -> 72.6% (+3.9) and judgment NDCG 70.1 -> 76.3.
- Single-sample generation pass@1 improves 65.4% -> 68.5% (+3.1) on LCB v6 without any direct generation reward.
- SFT on the same ranking data (teacher Qwen3-235B-Thinking) improves judgment (NDCG 70.1 -> 73.6) but leaves pass@1 at 65.4%, while GRPO improves both.
Surprising findings
- Training only on ranking rewards yields stronger code generation (pass@1 68.3%) than training directly on binary execution pass/fail reward (67.1%).
- SFT on teacher rankings improves judgment but does not transfer to generation, whereas on-policy GRPO does.
Limitations
- Relies on execution-grounded correctness, so it is less directly applicable to open-ended generation tasks.
- Effectiveness depends on mixed-quality candidate groups; too-weak or too-strong models yield little signal.
- Test suites may be imperfect, introducing label noise; mechanism of transfer only partially understood.
Experimental setup
Datasets: rSTARcoder seed subset LiveCodeBench v6 LiveCodeBench v5
Benchmarks: LiveCodeBench v6 LiveCodeBench v5
Metrics: Best-of-4 accuracy pass@1 NDCG
Baselines: OpenReasoning-Nemotron-32B TinyR1-32B OpenCodeReasoning-1.1-32B OpenReasoning-Nemotron-14B OpenCodeReasoning-1.1-14B OpenReasoning-Nemotron-7B Klear-Reasoner-8B DeepSeek-R1-0528-Qwen3-8B OpenCodeReasoning-1.1-7B Skywork-OR1-7B
Builds on: GRPO rSTARcoder LiveCodeBench veRL
Closest papers by meaning
- Test-Time Scaling in the Wild: Why Exploitation, Not Exploration, Is the Bottleneck (NeurIPS 2026 · similarity 0.88)
- CodeChemist: Test-Time Scaling for Low-Resource Code Generation via Functional Knowledge Transfer (ICML 2026 · similarity 0.87)
- CodeScaler: Scaling Code LLM Training and Test-Time Inference via Reward Models (NeurIPS 2026 · similarity 0.87)
- From Mathematical Reasoning to Code: Generalization of Process Reward Models in Test-Time Scaling (AAAI 2026 · similarity 0.87)
- Reasoning Through Execution: Unifying Process and Outcome Rewards for Code Generation (ICML 2025 · similarity 0.87)
- V1: Unifying Generation and Self-Verification for Parallel Reasoners (ICML 2026 · similarity 0.86)
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