Large Language Models Require Curated Context for Reliable Political Fact-Checking—Even with Reasoning and Web Search

Matthew R. DeVerna, Kai-Cheng Yang, Harry Yaojun Yan, Filippo Menczer


Abstract
Large language models (LLMs) have raised hopes for automated end-to-end fact-checking, but prior studies report mixed results. As mainstream chatbots increasingly ship with reasoning capabilities and web search tools—and millions of users already rely on them for verification—rigorous evaluation is urgent. We evaluate 15 recent LLMs from OpenAI, Google, Meta, and DeepSeek on more than 6,000 claims fact-checked by PolitiFact, comparing standard models with reasoning- and web-search variants. Standard models perform poorly, reasoning offers minimal benefits, and web search provides only moderate gains, despite fact-checks being available on the web. In contrast, a curated RAG system using PolitiFact summaries improved macro F1 by 233% on average across model variants. These findings suggest that giving models access to curated high-quality context is a promising path for automated fact-checking.
Anthology ID:
2026.findings-acl.1467
Volume:
Findings of the Association for Computational Linguistics: ACL 2026
Month:
July
Year:
2026
Address:
San Diego, California, United States
Editors:
Maria Liakata, Viviane P. Moreira, Jiajun Zhang, David Jurgens
Venue:
Findings
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Publisher:
Association for Computational Linguistics
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Pages:
29338–29360
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URL:
https://preview.aclanthology.org/ingest-acl/2026.findings-acl.1467/
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Cite (ACL):
Matthew R. DeVerna, Kai-Cheng Yang, Harry Yaojun Yan, and Filippo Menczer. 2026. Large Language Models Require Curated Context for Reliable Political Fact-Checking—Even with Reasoning and Web Search. In Findings of the Association for Computational Linguistics: ACL 2026, pages 29338–29360, San Diego, California, United States. Association for Computational Linguistics.
Cite (Informal):
Large Language Models Require Curated Context for Reliable Political Fact-Checking—Even with Reasoning and Web Search (DeVerna et al., Findings 2026)
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https://preview.aclanthology.org/ingest-acl/2026.findings-acl.1467.pdf
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