PAR2-RAG: Planned Active Retrieval and Reasoning for Multi-Hop Question Answering

Large language models (LLMs) remain brittle on multi-hop question answering (MHQA), where answering requires combining evidence across documents through retrieval and reasoning. Iterative retrieval systems can fail by locking onto an early low-recall trajectory and amplifying downstream errors, while planning-only approaches may produce static query sets that cannot adapt when intermediate evidence changes. We propose Planned Active Retrieval and Reasoning RAG (PAR2-RAG), a two-stage framework that separates coverage from commitment. PAR2-RAG first performs breadth-first anchoring to build a high-recall evidence frontier, then applies depth-first refinement with evidence sufficiency control in an iterative loop. Across four MHQA benchmarks, PAR2-RAG consistently outperforms existing state-of-the-art baselines, compared with IRCoT, PAR2-RAG achieves up to 23.5% higher accuracy, with retrieval gains of up to 10.5% in NDCG.