Paper: Reinforcement Learning without Ground-Truth Solutions can Improve LLMs
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Problem
Reinforcement learning (RL) has shown promise in improving large language models (LLMs). However, current RL methods often rely on having “ground-truth” answers to accurately reward the LLM’s performance. This severely limits their usefulness in situations where such ground truth is unavailable – a common scenario when dealing with tasks that involve complex problem-solving or code generation.
Method
The paper introduces a framework called RiVER (Ranking-induced VERifiable). The key innovation here is training LLMs on “score-based optimization tasks” rather than requiring ground-truth solutions. This means the model learns to improve based on execution feedback, specifically using scores as rewards – without needing to know the perfect answer upfront. The authors identified two issues when applying this approach: scale dominance (where different scores are skewed) and frequency dominance (where frequently sampled weaker solutions dominate learning). RiVER tackles these with a technique called “calibrated reward shaping” which uses comparisons between instances, emphasizing high-scoring solutions while still providing feedback for other valid results.



