RM-Bench: Benchmarking Reward Models of Language Models with Subtlety
  and Style
Authors: name: Yantao Liu, name: Zijun Yao, name: Rui Min, name: Yixin Cao, name: Lei Hou, name: Juanzi Li

Reward models are critical in techniques like Reinforcement Learning from
Human Feedback (RLHF) and Inference Scaling Laws, where they guide language
model alignment and select optimal responses. Despite their importance,
existing reward model benchmarks often evaluate models by asking them to
distinguish between responses generated by models of varying power. However,
this approach fails to assess reward models on subtle but critical content
changes and variations in style, resulting in a low correlation with policy
model performance. To this end, we introduce RM-Bench, a novel benchmark
designed to evaluate reward models based on their sensitivity to subtle content
differences and resistance to style biases. Extensive experiments demonstrate
that RM-Bench strongly correlates with policy model performance, making it a
reliable reference for selecting reward models to align language models
effectively. We evaluate nearly 40 reward models on RM-Bench. Our results
reveal that even state-of-the-art models achieve an average performance of only
46.6%, which falls short of random-level accuracy (50%) when faced with style
bias interference. These findings highlight the significant room for
improvement in current reward models. Related code and data are available at
https://github.com/THU-KEG/RM-Bench.