Odysseas S. Chlapanis

Odysseas S. Chlapanis

PhD student at AUEB · Affiliate researcher at Archimedes AI, Athena RC

AUEB Archimedes AI, Athena RC

I am a PhD student at the Athens University of Economics and Business and an affiliate researcher at Archimedes AI, Athena RC. My work centers on evaluating and improving how large language models reason over legal text: measuring their legal reasoning and citation faithfulness, and building practical, grounded LLM applications for law. I am also interested in what cognitive science reveals about how these models represent meaning.


Publications

2026

The Grounding Gap: How LLMs Anchor the Meaning of Abstract Concepts Differently from Humans

Odysseas S. Chlapanis, Orfeas Menis Mastromichalakis, Christos H. Papadimitriou

Preprint, arXiv:2605.08837, 2026

2025

GreekBarBench: A Challenging Benchmark for Free-Text Legal Reasoning and Citations

Odysseas S. Chlapanis, Dimitrios Galanis, Nikolaos Aletras, Ion Androutsopoulos

Findings of the ACL: EMNLP 2025, Suzhou, China

AUEB-Archimedes at RIRAG-2025: Is Obligation concatenation really all you need?

Ioannis Chasandras, Odysseas S. Chlapanis, Ion Androutsopoulos

1st Regulatory NLP Workshop (RegNLP 2025), pp. 52-58, Abu Dhabi, UAE

2024

LAR-ECHR: A New Legal Argument Reasoning Task and Dataset for Cases of the European Court of Human Rights

Odysseas S. Chlapanis, Dimitrios Galanis, Ion Androutsopoulos

Natural Legal Language Processing Workshop (NLLP 2024), Miami, FL

Miami, host city of NLLP 2024

Local Explanations and Self-Explanations for Assessing Faithfulness in Black-box LLMs

Christos Fragkathoulas, Odysseas S. Chlapanis

13th EETN Conference on AI (SETN 2024) Workshops

Archimedes-AUEB at SemEval-2024 Task 5: LLM explains Civil Procedure

Odysseas S. Chlapanis, Ion Androutsopoulos, Dimitrios Galanis

18th International Workshop on Semantic Evaluation (SemEval-2024), Mexico City

Mexico City, host of SemEval-2024
2023

Adapted Multimodal BERT with Layer-wise Fusion for Sentiment Analysis

Odysseas S. Chlapanis, Georgios Paraskevopoulos, Alexandros Potamianos

IEEE ICASSP 2023, Rhodes Island, Greece

Rhodes, host of IEEE ICASSP 2023

Experience

Research Visit, Columbia University

Visited Columbia University to work with Professor Christos H. Papadimitriou on how large language models anchor the meaning of abstract words. This collaboration led to the paper The Grounding Gap: How LLMs Anchor the Meaning of Abstract Concepts Differently from Humans.


Mentoring & Outreach

Panhellenic Artificial Intelligence Competition

Greece's national Artificial Intelligence competition for high-school students. I help design the competition tasks and mentor the students selected to represent Greece at the international competitions.


Writing

Gemini-3 Benchmarkathon Blog

A Hugging Face community report benchmarking Gemini-3 on legal tasks, including GreekBarBench. I contributed as part of the team.