Detecting Post-generation Edits to Watermarked LLM Outputs via Error-Correcting Codes

Zewei Deng, Muhammad Siddeek, Liyan Xie, Mohamed Mohamed, Mengdi Wang, H. Vincent Poor, Andrea Goldsmith


Abstract
Watermarking has become a key mechanism for distinguishing AI-generated from human-written texts. In practical settings, however, content produced by large language models (LLMs) is often subject to critical post-generation edits, posing challenges for detecting and localizing such modifications. In this work, we propose incorporating error-correcting codes, specifically Varshamov-Tenengolts (VT) codes, by embedding VT code strings into watermarked LLM outputs, thus enabling post-generation edit detection of token insertions and deletions. We accompany such a watermarking procedure with a watermark detector and a post-edit detector. We evaluate our method on open-source LLM using synthetic edits and demonstrate excellent empirical performance of post-generation edit detection.
Anthology ID:
2026.findings-emnlp.2142
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
45788–45796
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.2142/
DOI:
Bibkey:
Cite (ACL):
Zewei Deng, Muhammad Siddeek, Liyan Xie, Mohamed Mohamed, Mengdi Wang, H. Vincent Poor, and Andrea Goldsmith. 2026. Detecting Post-generation Edits to Watermarked LLM Outputs via Error-Correcting Codes. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 45788–45796, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Detecting Post-generation Edits to Watermarked LLM Outputs via Error-Correcting Codes (Deng et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.2142.pdf