Digital watermarking refers to the embedding of imperceptible or barely perceptible information into digital media such as images, audio, video, or text. The embedded information can encode authorship, provenance, integrity, or other metadata and remains associated with the content as it is distributed or processed.
The emergence of large language models (LLMs) has enabled the generation of high-quality synthetic text, often indistinguishable from human-written content, at a scale that may substantially affect the information ecosystem. Text watermarking offers one possible approach to identifying and labelling LLM-generated content. It poses a particular challenge, though: unlike images or audio, where information can often be embedded by modifying an underlying signal, watermarking text necessarily involves altering the text itself. This creates a trade-off between detectability and textual quality.
This talk introduces and illustrates two approaches to text watermarking: generative watermarking, in which the watermark is incorporated during text generation, and post-hoc watermarking, in which it is added to existing text. I will also explore related problems and challenges.
For communication, please join the Discord Server (https://discord.gg/PEMh4a2YHV) and follow the #checkthat lab-channel.
Registration
Please register to participate in the CheckThat! Lab tasks.
Recent Updates
14 Sep, 2026: Program is online.
20 May, 2026: Gold labels for all test datasets are available.
15 May, 2026: All leaderboards are made public.
17 Apr, 2026: an online session will be conducted on 24th of April, 3pm CEST, giving a short overview on each task and a walk-through of the submission system.
17 Apr, 2026: Submission site URLs for Task 1 and 2 are available. Please check task specific page.
@InProceedings{10.1007/978-3-032-21321-1_43,
author="Stru{\ss}, Julia Maria
and Schellhammer, Sebastian
and Dietze, Stefan
and V., Venktesh
and Setty, Vinay
and Chakraborty, Tanmoy
and Nakov, Preslav
and Anand, Avishek
and Chungkham, Primakov
and Hafid, Salim
and Sahnan, Dhruv
and Todorov, Konstantin",
editor="Campos, Ricardo
and Jatowt, Adam
and Lan, Yanyan
and Aliannejadi, Mohammad
and Bauer, Christine
and MacAvaney, Sean
and Anand, Avishek
and Ren, Zhaochun
and Verberne, Suzan
and Bai, Nan
and Mansoury, Masoud",
title="The CLEF-2026 CheckThat! Lab: Advancing Multilingual Fact-Checking",
booktitle="Advances in Information Retrieval",
year="2026",
publisher="Springer Nature Switzerland",
address="Cham",
pages="325--335",
isbn="978-3-032-21321-1"
}
CLEF 2026 LNCS
@InProceedings{clef-checkthat:2026-lncs,
author = {
Stru{\ss}, Julia Maria
and Schellhammer, Sebastian
and Dietze, Stefan
and V., Venktesh
and Setty, Vinay
and Chakraborty, Tanmoy
and Nakov, Preslav
and Anand, Avishek
and Chungkham, Primakov
and Hafid, Salim
and Sahnan, Dhruv
and Todorov, Konstantin},
title = {Overview of the {CLEF}-2026 {CheckThat! Lab}: Advancing Multilingual Fact-Checking},
editor = {
Hagen, Matthias
and Potthast, Martin
and Stein, Benno
and Schaer, Philipp
and Zangerle, Eva
and MacAvaney, Sean
and Stru{\ss}, Julia Maria
and Salido, Eva S{\'a}nchez
and Barr{\'o}n-Cede{\~n}o, Alberto
and {Alba Garc{\'i}a Seco de Herrera}},
publisher = {Springer},
booktitle = {Experimental IR Meets Multilinguality, Multimodality, and Interaction. Proceedings of the Seventeenth International Conference of the CLEF Association (CLEF 2026)},
year = {2026}
}
CLEF 2026 CEUR papers
Here you find the task-specific papers. They all cross-ref to include information about the volume:
@proceedings{clef2026-workingnotes,
title = {{CLEF} 2026 Working Notes},
editor = {
Salido, Eva S{\'a}nchez
and Barr{\'o}n-Cede{\~n}o, Alberto
and {Alba Garc{\'i}a Seco de Herrera}
and MacAvaney, Sean
and Stru{\ss}, Julia Maria},
series = {CLEF~2026},
address = {Jena, Germany},
year = 2026
}
Task 1
@inproceedings{clef-checkthat:2026:task1,
title = {Overview of the {CLEF-2026 CheckThat!} Lab Task 1 on
Source Retrieval for Scientific Web Claims},
author = {
Schellhammer, Sebastian and
Hafid, Salim and
Kartal, Yavuz Selim and
Boland, Katarina and
Dimitrov, Dimitar and
Todorov, Konstantin and
Dietze, Stefan
},
crossref = {clef2026-workingnotes}
}
Task 2
@inproceedings{clef-checkthat:2026:task2,
title = {Overview of the {CLEF-2026 CheckThat!} Lab Task 2 on
Fact-Checking Numerical Claims},
author = {
V, Venktesh and
Setty, Vinay and
Chungkham, Primakov and
Anand, Avishek and
Alam, Firoj
},
crossref = {clef2026-workingnotes}
}
Task 3
@inproceedings{clef-checkthat:2026:task3,
title = {Overview of the {CLEF-2026 CheckThat!} Lab Task 3 on
Generating Full Fact-Checking Articles},
author = {
Sahnan, Dhruv and Chakraborty, Tanmoy and Nakov, Preslav
},
crossref = {clef2026-workingnotes}
}
