Expert Evaluation of LLM's Open-Ended Legal Reasoning on the Japanese Bar Exam Writing Task

Computer Science > Artificial Intelligence arXiv:2604.23730 (cs) [Submitted on 26 Apr 2026] Title:Expert Evaluation of LLM's Open-Ended Legal Reasoning on the Japanese Bar Exam Writing Task Authors:Jungmin Choi, Keisuke Sakaguchi, Hiroaki Yamada View a PDF of the paper titled Expert Evaluation of LLM's Open-Ended Legal Reasoning on the Japanese Bar Exam Writing Task, by Jungmin Choi and 2 other authors View PDF HTML (experimental) Abstract:Large language models (LLMs) have shown strong performance on legal benchmarks, including multiple-choice components of bar exams. However, their capacity for generating open-ended legal reasoning in realistic scenarios remains insufficiently explored. Notably, to our best knowledge, there are no prior studies or datasets addressing this issue in the Japanese context. This study presents the first dataset designed to evaluate the open-ended legal reasoning performance of LLMs within the Japanese jurisdiction. The dataset is based on the writing component of the Japanese bar examination, which requires examinees to identify multiple legal issues from long narratives and to construct structured legal arguments in free text format. Our key contribution is the manual evaluation of LLMs' generated responses by legal experts, which reveals limitations and challenges in legal reasoning. Moreover, we conducted a manual analysis of hallucinations to characterize when and how the models introduce content not supported by precedent or law. Our real exam questions, model-generated responses, and expert evaluations reveal the milestones of current LLMs in the Japanese legal domain. Our dataset and relevant resources will be available online. Comments: 5 pages, Accepted to ICAIL 2026 Subjects: Artificial Intelligence (cs.AI) Cite as: arXiv:2604.23730 [cs.AI] (or arXiv:2604.23730v1 [cs.AI] for this version) https://doi.org/10.48550/arXiv.2604.23730 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Jungmin Choi [view email] [v1] Sun, 26 Apr 2026 14:15:43 UTC (80 KB) Full-text links: Access Paper: View a PDF of the paper titled Expert Evaluation of LLM's Open-Ended Legal Reasoning on the Japanese Bar Exam Writing Task, by Jungmin Choi and 2 other authorsView PDFHTML (experimental)TeX Source view license Current browse context: cs.AI < prev | next > new | recent | 2026-04 Change to browse by: cs References & Citations NASA ADSGoogle Scholar Semantic Scholar export BibTeX citation Loading... BibTeX formatted citation × loading... Data provided by: Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Code, Data and Media Associated with this Article alphaXiv Toggle alphaXiv (What is alphaXiv?) Links to Code Toggle CatalyzeX Code Finder for Papers (What is CatalyzeX?) DagsHub Toggle DagsHub (What is DagsHub?) GotitPub Toggle Gotit.pub (What is GotitPub?) Huggingface Toggle Hugging Face (What is Huggingface?) ScienceCast Toggle ScienceCast (What is ScienceCast?) Demos Demos Replicate Toggle Replicate (What is Replicate?) Spaces Toggle Hugging Face Spaces (What is Spaces?) Spaces Toggle TXYZ.AI (What is TXYZ.AI?) Related Papers Recommenders and Search Tools Link to Influence Flower Influence Flower…

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