Personalization over Generalization: History-Aware Sentence-Level AI Detection in Collaborative Writing

Rizky Adi, Yoshimi Suzuki, Fumiyo Fukumoto


Abstract
Sentence-level AI detectors are essential for detecting AI misuse in human-AI collaborative writing. Yet existing approaches still treat all authors identically, ignoring individual writing styles. This is a critical oversight, given that the boundary between human and AI text is inherently author-specific. To address this limitation, we propose PHAS-ID (Personalized History-Aware Sentence-level AI Detector), an approach that introduces personalization to sentence-level detection. By matching target sentences against the author’s history of labeled documents, PHAS-ID tailors its predictions based on prior writing behaviors. Furthermore, current synthetic datasets for this task fail to capture realistic collaborative patterns, which we address by introducing GhostFill, a style-aware synthetic dataset generation pipeline. Our experiments demonstrate that PHAS-ID outperforms the previous state-of-the-art (SOTA) across seen-author, unseen-author, cross-domain, and cross-generator settings. Ablation studies confirm that these improvements stem from genuine author-specific personalization rather than the mere addition of context. Our source code and dataset are available at our GitHub repository.
Anthology ID:
2026.emnlp-main.1282
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
Note:
Pages:
29217–29235
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1282/
DOI:
Bibkey:
Cite (ACL):
Rizky Adi, Yoshimi Suzuki, and Fumiyo Fukumoto. 2026. Personalization over Generalization: History-Aware Sentence-Level AI Detection in Collaborative Writing. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 29217–29235, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Personalization over Generalization: History-Aware Sentence-Level AI Detection in Collaborative Writing (Adi et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1282.pdf