How Retrieval Credit Is Assigned Decides Search-Agent Training Gains: Local Credit Lifts Qwen3-4B Average F1 from 51.25 to 54.34
The study builds corpus-grounded QA data with intermediate evidence annotations and compares three retrieval signals (evidence coverage Cov, coverage with dependencies Cov-Dep, answer match AM) under scalar reward bonuses versus action-aligned local credit, training Qwen3-4B on seven QA benchmarks and finding local credit outperforms scalar, with Cov-local reaching 54.34 average F1 versus 51.25 for outcome-only training.