arXiv — NLP / Computation & Language · · 3 min read

Is a Document Educational or Just Wikipedia-Style? -- Pitfalls of Classifier-Based Quality Filtering

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Computer Science > Computation and Language

arXiv:2605.23721 (cs)
[Submitted on 21 May 2026]

Title:Is a Document Educational or Just Wikipedia-Style? -- Pitfalls of Classifier-Based Quality Filtering

View a PDF of the paper titled Is a Document Educational or Just Wikipedia-Style? -- Pitfalls of Classifier-Based Quality Filtering, by Mateusz Klimaszewski and 1 other authors
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Abstract:Classifier-based Quality Filtering has recently emerged as a fundamental technique in constructing pre-training corpora. The ability to deploy a single model that can replace or supplement a set of heuristics has proven effective across numerous Large Language Models. In this work, we expose a critical vulnerability in this approach by demonstrating how a straightforward Wikipedia-style reformatting operation can substantially alter a model's quality assessment and enable low-quality content to surpass filtering thresholds. Our analysis reveals that the FineWeb-Edu CQF model would reverse its filtering decision for approximately 7% of evaluated documents, thereby admitting content into the pre-training corpus that would otherwise have been excluded.
Comments: Accepted to ACL 2026
Subjects: Computation and Language (cs.CL)
Cite as: arXiv:2605.23721 [cs.CL]
  (or arXiv:2605.23721v1 [cs.CL] for this version)
  https://doi.org/10.48550/arXiv.2605.23721
arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Mateusz Klimaszewski [view email]
[v1] Thu, 21 May 2026 08:59:11 UTC (10,972 KB)
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