Probing Pretraining “Quality”: Sociolinguistic Mobility as a Lens on Web Corpus Filters

Jessica Wang


Abstract
Data selection algorithms for large language model (LLM) pretraining are designed to mine ‘quality’ from the web, but that notion is murky at best. This study explores whether sociolinguistic mobility – realized through language use, in context – offers a lens for understanding what such algorithms actually select. As a case study, the FineWeb pretraining pipeline is examined for how it reshapes two tangible axes of language use: the geographical provenance and register composition of texts drawn from ICE and GloWbE.

FineWeb rejection rates are highest, and fairly uniform across provenance groups, for web-native and high-context registers (90.9% and 99.2%, respectively) but within medium-context registers, association with the United States is moderately protective: the 7% rejection rate is well below the medium-context average of 38%, an effect corroborated by NPMI. Unlike prior work on learned, classifier-based filters and US-internal sociolect bias, this study finds comparable effects in a deterministic pipeline within the global spread of English. As pretraining data selection becomes increasingly opaque, these results suggest that algorithmic ‘quality’ does not represent a real-world range of English use manifested in the web-as-corpus – a gap made visible by tangible sociolinguistic dimensions.
Anthology ID:
2026.wac-1.28
Volume:
Proceedings of the 13th Web-as-Corpus Workshop
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Pedro Ortiz Suarez, Laurie Burchell, Nikola Ljubešić, Yves Scherrer, Veronika Laippala, Vuk Dinić, Thom Vaughan
Venues:
WAC | WS
SIG:
SIGWAC
Publisher:
Association for Computational Linguistics
Note:
Pages:
320–330
Language:
URL:
https://aclanthology.org/2026.wac-1.28/
DOI:
Bibkey:
Cite (ACL):
Jessica Wang. 2026. Probing Pretraining “Quality”: Sociolinguistic Mobility as a Lens on Web Corpus Filters. In Proceedings of the 13th Web-as-Corpus Workshop, pages 320–330, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Probing Pretraining “Quality”: Sociolinguistic Mobility as a Lens on Web Corpus Filters (Wang, WAC 2026)
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PDF:
https://aclanthology.org/2026.wac-1.28.pdf