Fathom: A Fast and Modular RAG Pipeline for Fact-Checking

Farrukh Bin Rashid, Saqib Hakak


Abstract
We present Fathom, a Retrieval-Augmented Generation (RAG) pipeline for automated fact-checking, built entirely using lightweight open-source language models. The system begins with HyDE-style question generation to expand the context around each claim, followed by a dual-stage retrieval process using BM25 and semantic similarity to gather relevant evidence. Finally, a lightweight LLM performs veracity prediction, producing both a verdict and supporting rationale. Despite relying on smaller models, our system achieved an AVeriTeC score of 0.2043 on the test set, a 0.99% absolute improvement over the baseline and 0.378 on the dev set, marking a 27.7% absolute improvement.
Anthology ID:
2025.fever-1.20
Volume:
Proceedings of the Eighth Fact Extraction and VERification Workshop (FEVER)
Month:
July
Year:
2025
Address:
Vienna, Austria
Editors:
Mubashara Akhtar, Rami Aly, Christos Christodoulopoulos, Oana Cocarascu, Zhijiang Guo, Arpit Mittal, Michael Schlichtkrull, James Thorne, Andreas Vlachos
Venues:
FEVER | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
258–265
Language:
URL:
https://preview.aclanthology.org/landing_page/2025.fever-1.20/
DOI:
Bibkey:
Cite (ACL):
Farrukh Bin Rashid and Saqib Hakak. 2025. Fathom: A Fast and Modular RAG Pipeline for Fact-Checking. In Proceedings of the Eighth Fact Extraction and VERification Workshop (FEVER), pages 258–265, Vienna, Austria. Association for Computational Linguistics.
Cite (Informal):
Fathom: A Fast and Modular RAG Pipeline for Fact-Checking (Rashid & Hakak, FEVER 2025)
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PDF:
https://preview.aclanthology.org/landing_page/2025.fever-1.20.pdf