J1: Exploring Simple Test-Time Scaling for LLM-as-a-Judge

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Hauptverfasser: Chan, Chi-Min, Xu, Chunpu, Ji, Jiaming, Ye, Zhen, Wen, Pengcheng, Jiang, Chunyang, Yang, Yaodong, Xue, Wei, Han, Sirui, Guo, Yike
Format: Preprint
Veröffentlicht: 2025
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author Chan, Chi-Min
Xu, Chunpu
Ji, Jiaming
Ye, Zhen
Wen, Pengcheng
Jiang, Chunyang
Yang, Yaodong
Xue, Wei
Han, Sirui
Guo, Yike
author_facet Chan, Chi-Min
Xu, Chunpu
Ji, Jiaming
Ye, Zhen
Wen, Pengcheng
Jiang, Chunyang
Yang, Yaodong
Xue, Wei
Han, Sirui
Guo, Yike
contents The current focus of AI research is shifting from emphasizing model training towards enhancing evaluation quality, a transition that is crucial for driving further advancements in AI systems. Traditional evaluation methods typically rely on reward models assigning scalar preference scores to outputs. Although effective, such approaches lack interpretability, leaving users often uncertain about why a reward model rates a particular response as high or low. The advent of LLM-as-a-Judge provides a more scalable and interpretable method of supervision, offering insights into the decision-making process. Moreover, with the emergence of large reasoning models, which consume more tokens for deeper thinking and answer refinement, scaling test-time computation in the LLM-as-a-Judge paradigm presents an avenue for further boosting performance and providing more interpretability through reasoning traces. In this paper, we introduce $\textbf{J1-7B}$, which is first supervised fine-tuned on reflection-enhanced datasets collected via rejection-sampling and subsequently trained using Reinforcement Learning (RL) with verifiable rewards. At inference time, we apply Simple Test-Time Scaling (STTS) strategies for additional performance improvement. Experimental results demonstrate that $\textbf{J1-7B}$ surpasses the previous state-of-the-art LLM-as-a-Judge by $ \textbf{4.8}$\% and exhibits a $ \textbf{5.1}$\% stronger scaling trend under STTS. Additionally, we present three key findings: (1) Existing LLM-as-a-Judge does not inherently exhibit such scaling trend. (2) Model simply fine-tuned on reflection-enhanced datasets continues to demonstrate similarly weak scaling behavior. (3) Significant scaling trend emerges primarily during the RL phase, suggesting that effective STTS capability is acquired predominantly through RL training.
format Preprint
id arxiv_https___arxiv_org_abs_2505_11875
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle J1: Exploring Simple Test-Time Scaling for LLM-as-a-Judge
Chan, Chi-Min
Xu, Chunpu
Ji, Jiaming
Ye, Zhen
Wen, Pengcheng
Jiang, Chunyang
Yang, Yaodong
Xue, Wei
Han, Sirui
Guo, Yike
Machine Learning
Computation and Language
The current focus of AI research is shifting from emphasizing model training towards enhancing evaluation quality, a transition that is crucial for driving further advancements in AI systems. Traditional evaluation methods typically rely on reward models assigning scalar preference scores to outputs. Although effective, such approaches lack interpretability, leaving users often uncertain about why a reward model rates a particular response as high or low. The advent of LLM-as-a-Judge provides a more scalable and interpretable method of supervision, offering insights into the decision-making process. Moreover, with the emergence of large reasoning models, which consume more tokens for deeper thinking and answer refinement, scaling test-time computation in the LLM-as-a-Judge paradigm presents an avenue for further boosting performance and providing more interpretability through reasoning traces. In this paper, we introduce $\textbf{J1-7B}$, which is first supervised fine-tuned on reflection-enhanced datasets collected via rejection-sampling and subsequently trained using Reinforcement Learning (RL) with verifiable rewards. At inference time, we apply Simple Test-Time Scaling (STTS) strategies for additional performance improvement. Experimental results demonstrate that $\textbf{J1-7B}$ surpasses the previous state-of-the-art LLM-as-a-Judge by $ \textbf{4.8}$\% and exhibits a $ \textbf{5.1}$\% stronger scaling trend under STTS. Additionally, we present three key findings: (1) Existing LLM-as-a-Judge does not inherently exhibit such scaling trend. (2) Model simply fine-tuned on reflection-enhanced datasets continues to demonstrate similarly weak scaling behavior. (3) Significant scaling trend emerges primarily during the RL phase, suggesting that effective STTS capability is acquired predominantly through RL training.
title J1: Exploring Simple Test-Time Scaling for LLM-as-a-Judge
topic Machine Learning
Computation and Language
url https://arxiv.org/abs/2505.11875