arXiv Machine Learning By M\'elissa Tamine, Otmane Sakhi, Benjamin Heymann, Maxime Vono, Patrick Loiseau

Shapley-based Data Valuation for LLM Alignment via Sequential Preference Optimization

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arXiv:2512. 15765v3 Announce Type: replace Abstract: Data valuation is a natural framework for understanding which preference datasets matter most when aligning a Large Language Model (LLM) using multiple sources.

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arXiv AI
Sep 17

A Zeroth-Order Paradigm for LLM Preference Alignment

The paper introduces Comparison-based Preference Optimization (ComPO), a zeroth-order method that aligns large language models with human preferences using comparison oracles instead of direct differentiable loss optimization. It provides theoretical convergence guarantees for both offline and online variants under smoothness, gradient sparsity, and oracle compatibility assumptions, and establishes performance bounds under local coverage and in-distribution reward accuracy. Experiments on several LLMs (Mistral, Llama, Gemma-2, Qwen3, Gemma-3) show that ComPO outperforms existing direct alignment methods, achieving higher length-controlled win rates and diagnostics that suggest mitigation of likelihood displacement.

By Peter Chen, Xi Chen, Wotao Yin, Tianyi Lin