CAST: An Interpretable Evidence-Based Confidence Estimation Tool for RAG with Human-in-the-Loop Verification

Xutong Liu, Morris Groot Beumer, Joerg Robert Osterrieder, Max Baak


Abstract
Large language models (LLMs) increasingly assist financial analysis tasks over filings, reports, and news via retrieval-augmented generation (RAG), but a human reviewer typically remains accountable for the final decision. In this setting, a confidence score must be more than well-calibrated: it must be evidence-based and explainable, so reviewers can see why an answer should be trusted. We introduce CAST (Confidence via Answer Support Testing), a Bayesian-inspired confidence method that compares a generated answer with a plausible competing alternative and evaluates how retrieved passages support each hypothesis. CAST produces both an answer-level confidence score and citation-level evidence for review. We also demonstrate CAST through an interactive reviewer-facing tool that visualizes supporting and opposing evidence for human verification. On 1,286 financial-report questions from MMDocRAG, CAST achieves the highest AUROC among seven evaluated methods (0.634 vs. 0.598 for the strongest baseline).
Anthology ID:
2026.finnlp-1.26
Volume:
Proceedings of the 11th Workshop on Financial Technology and Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Jimin Huang, Yongjae Lee, Sophia Ananiadou, Hsin-Hsi Chen, Hiroya Takamura, Chung-Chi Chen
Venues:
FinNLP | WS
SIG:
SIGFinTech
Publisher:
Association for Computational Linguistics
Note:
Pages:
332–341
Language:
URL:
https://aclanthology.org/2026.finnlp-1.26/
DOI:
Bibkey:
Cite (ACL):
Xutong Liu, Morris Groot Beumer, Joerg Robert Osterrieder, and Max Baak. 2026. CAST: An Interpretable Evidence-Based Confidence Estimation Tool for RAG with Human-in-the-Loop Verification. In Proceedings of the 11th Workshop on Financial Technology and Natural Language Processing, pages 332–341, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
CAST: An Interpretable Evidence-Based Confidence Estimation Tool for RAG with Human-in-the-Loop Verification (Liu et al., FinNLP 2026)
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PDF:
https://aclanthology.org/2026.finnlp-1.26.pdf