MiCRo: Mixture Modeling and Context-aware Routing for Personalized
  Preference Learning
Authors: name: Jingyan Shen; name: Jiarui Yao; name: Rui Yang; name: Yifan Sun; name: Feng Luo; name: Rui Pan; name: Tong Zhang; name: Han Zhao
Published: 2025-05-30 17:44:28

Abstract: Reward modeling is a key step in building safe foundation models when
applying reinforcement learning from human feedback (RLHF) to align Large
Language Models (LLMs). However, reward modeling based on the Bradley-Terry
(BT) model assumes a global reward function, failing to capture the inherently
diverse and heterogeneous human preferences. Hence, such oversimplification
limits LLMs from supporting personalization and pluralistic alignment.
Theoretically, we show that when human preferences follow a mixture
distribution of diverse subgroups, a single BT model has an irreducible error.
While existing solutions, such as multi-objective learning with fine-grained
annotations, help address this issue, they are costly and constrained by
predefined attributes, failing to fully capture the richness of human values.
In this work, we introduce MiCRo, a two-stage framework that enhances
personalized preference learning by leveraging large-scale binary preference
datasets without requiring explicit fine-grained annotations. In the first
stage, MiCRo introduces context-aware mixture modeling approach to capture
diverse human preferences. In the second stage, MiCRo integrates an online
routing strategy that dynamically adapts mixture weights based on specific
context to resolve ambiguity, allowing for efficient and scalable preference
adaptation with minimal additional supervision. Experiments on multiple
preference datasets demonstrate that MiCRo effectively captures diverse human
preferences and significantly improves downstream personalization.