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Legal Domain Adaptation of Modern BERT Models

Summary

Researchers further pre-trained ModernBERT on all US court opinions, achieving significant improvements over vanilla ModernBERT on legal tasks. Despite ModernBERT's 500x larger pre-training data compared to original BERT, domain adaptation still yields gains. From-scratch pre-training underperforms continued pre-training. The model handles up to 8,192 tokens and is useful for legal text embeddings or reranking. All checkpoints are released. To appear at ICAIL 2026.

SourcearXiv Computational LinguisticsAuthor: Dominik Stammbach, Peter Henderson
Legal Domain Adaptation of Modern BERT Models
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[2606.28538] Legal Domain Adaptation of Modern BERT Models

[Submitted on 26 Jun 2026]

Title:Legal Domain Adaptation of Modern BERT Models

View a PDF of the paper titled Legal Domain Adaptation of Modern BERT Models, by Dominik Stammbach and 1 other authors

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Abstract:We investigate domain adaptation of modern BERT models in the legal domain. We further pre-train ModernBERT on all US court opinions using the masked language modeling objective. Although ModernBERT has been trained on roughly 500x more data than original BERT, we still find that this model benefits from further pre-training and domain adaptation in the legal domain: we report significant improvements compared to vanilla ModernBERT on all datasets connected to US court opinions. We find gains similar to those reported in early work on domain adaptation of BERT-like models. However, from scratch pre-training does not match the performance of further pre-training an existing ModernBERT checkpoint in our experiments. The resulting models are capable of processing sequences up to 8,192 tokens, and can be used to compute meaningful embeddings of legal passages, or could quickly rerank hundreds of legal passages for a given search query. We release all model checkpoints publicly.

Comments: To appear in Proceedings of the 21st International Conference on Artificial Intelligence and Law (ICAIL 2026), June 9-12, 2026, Singapore

Subjects:

Computation and Language (cs.CL)

Cite as: arXiv:2606.28538 [cs.CL]

(or arXiv:2606.28538v1 [cs.CL] for this version)

https://doi.org/10.48550/arXiv.2606.28538

arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Dominik Stammbach [view email] [v1] Fri, 26 Jun 2026 18:44:11 UTC (186 KB)

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Key points and analysis

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Key points

  • Further pre-training ModernBERT on US court opinions via masked language modeling.
  • Significant performance gains on all US court opinions datasets over vanilla ModernBERT.
  • From-scratch pre-training does not match continued pre-training from existing checkpoint.
  • Model supports up to 8,192 tokens, useful for embeddings and fast reranking of legal passages.

Highlights and analysis are generated automatically and may contain errors. Check the original source.