Temporal Leakage in Financial News NLP: A Multi-Architecture Audit with a Regime-Specific M&A Signal

Chenhao Xue, Raslen Guesmi, Siwei Feng, Yucheng Gong, Jacob Xavier Sundram, Jordan Pang, Lan Wang, Julian Kaljuvee


Abstract
Financial-news direction prediction has become a popular NLP benchmark, yet reported gains depend critically on whether the train–test split is chronological or random, i.e., on temporal leakage. We audit this dependence on a 49,799-article corpus across 16 feature–model combinations spanning TF-IDF, MiniLM, FinBERT, and fine-tuned RoBERTa-large / DeBERTa-v3-large, plus separate zero/few-shot and LoRA probes of Llama-3 and Qwen2.5 LLMs: random splits inflate MCC by 1.1× to 6.5×, tracking model capacity and feature richness, and end-to-end FinBERT fine-tuning re-amplifies rather than closes the gap (size-matched ratio 1.75×). Conditioning on event type, mergers and acquisitions (M A) is the only audited category with a positive locked-test signal under near-temporal chronological evaluation (TF-IDF MCC = 0.138 train-only, 0.068 under train∪val refit; 10,000-permutation p < 10⁻³); the signal does not transfer to FNSPID’s 2009–2020 U.S. corpus, localising the headline to our 2024–2025 European-tilted M A semantics rather than a universal predictor. Three independent role labellers converge on acquirer-tagged articles as the signal locus, a power-limited qualitative convergence rather than a hypothesis-tested asymmetry. Chronological splitting plays for financial NLP the role characteristics-purging plays for asset pricing: it strips the predictable, stale component of news and leaves a residual that is small, event-localized, and lexically shallow. We advocate leakage audits as a required disclosure for financial-NLP benchmarks.
Anthology ID:
2026.emnlp-main.2386
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
54209–54242
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URL:
https://aclanthology.org/2026.emnlp-main.2386/
DOI:
Bibkey:
Cite (ACL):
Chenhao Xue, Raslen Guesmi, Siwei Feng, Yucheng Gong, Jacob Xavier Sundram, Jordan Pang, Lan Wang, and Julian Kaljuvee. 2026. Temporal Leakage in Financial News NLP: A Multi-Architecture Audit with a Regime-Specific M&A Signal. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 54209–54242, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Temporal Leakage in Financial News NLP: A Multi-Architecture Audit with a Regime-Specific M&A Signal (Xue et al., EMNLP 2026)
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https://aclanthology.org/2026.emnlp-main.2386.pdf