Re:CAP - Auditing Retrieval Coverage in Production RAG Pipelines

Aviral Joshi, Hanoz Bhathena, Max Nelson, Saket Sharma


Abstract
Retrieval-augmented generation (RAG) is hard to monitor in production: exhaustive relevance labels do not exist for non-stationary multi-million-passage corpora that re-index in real time. As a result, retrieval quality is generally understudied and often deprioritised in favour of generation-oriented metrics. In this work, we propose auditing retrieval coverage by probing for evidence of missing documents rather than enumerating every relevant one. Our method Re:CAP (REtrieval Coverage Audit by iterative Probing) is a reference-free audit loop applied to a deployed RAG pipeline’s initial answer and retrieved context: it identifies the topics already covered, generates probing questions for plausibly missing topics, retrieves candidate documents, and applies an LLM-as-judge to retain only those that introduce previously-unretrieved information. On four public benchmarks, Re:CAP recovers 9–29% of gold labels that flat BM25 top-500 cannot reach, rising to 48% on TREC-COVID. On MuSiQue Re:CAP beats flat hybrid top-500 by +12.9 pp on recall at less than half the document budget. An ensemble BM25, dense, and hybrid baseline (top-500 each) still leaves out 21.2% of gold docs on TREC-COVID that Re:CAP recovers; human annotators judge that 78.9% of those structurally distinct documents add new information to the baseline answer (Fleiss κ = 0.79, n = 123), and 73.9% on live production traffic (n = 180). End-to-end recall is reproducible to within ±1% across three independent runs, making Re:CAP a stable instrument for periodic retrieval audits.
Anthology ID:
2026.emnlp-industry.150
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing: Industry Track
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Pepa Atanasova, Gholamreza Haffari, Minghan Wang
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
2532–2565
Language:
URL:
https://aclanthology.org/2026.emnlp-industry.150/
DOI:
Bibkey:
Cite (ACL):
Aviral Joshi, Hanoz Bhathena, Max Nelson, and Saket Sharma. 2026. Re:CAP - Auditing Retrieval Coverage in Production RAG Pipelines. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing: Industry Track, pages 2532–2565, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Re:CAP - Auditing Retrieval Coverage in Production RAG Pipelines (Joshi et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-industry.150.pdf