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Search Arena Meets Nuggets: Towards Explanations and Diagnostics in the Evaluation of LLM Responses

Sahel Sharifymoghaddam, Shivani Upadhyay, Nandan Thakur, Ronak Pradeep, Jimmy Lin

International Conference on the Theory of Information Retrieval, 2026

Abstract

Side-by-side comparisons that elicit human preferences are commonly used to assess the quality of large language model (LLM) output and have been applied to retrieval-augmented generation (RAG) systems. However, when applied to complex, information-seeking queries, these methods are limited by their inability to provide explanatory or diagnostic insights. As an alternative, nugget-based evaluations that decompose long-form answers into atomic facts have emerged as a promising strategy for RAG evaluation. In this work, we employ AutoNuggetizer, a nugget-based framework, to analyze ?5K Search Arena battles from LMArena by automatically generating and assigning nuggets, converting each model response into a quantitative score. We observe strong alignment between nugget-based Elo rankings and human preferences, exceeding the corresponding alignment achieved by LLM-as-a-judge with chain-of- thought (CoT) evaluation, while substantially reducing the number of preference inversions. Furthermore, we provide in-depth analyses including inversions, nugget quality, and shared-blindness effects. All our code is available at https://github.com/castorini/SxSNuggets.

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