Author

Yan-Sen Han

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Preprint Aug 2026

Manifold Drift in Flow Preference Optimization: A Root Cause of Reward Hacking

Preference optimization is a standard alignment method for generative models, yet extending it to continuous-time dynamics remains non-trivial. In flow matching, reward-driven updates modify transport trajectories without an inherent constraint to the pretrained data manifold and can move terminal samples off the pretr...

Yan-Sen Han, Shengyi Liao, Yuan-Xing Zhang et al. · 0 citations

#artificial intelligence Preprint Sep 2026

FlowCPO: A Unified Divergence View of Preference Alignment for Flow Models

This work introduces FlowCPO, an offline forward-KL objective that uses both preferred and dispreferred samples without online rollouts and shows under explicit regularity conditions that the forward-KL objective is bounded by a contrastive flow matching loss, yielding a tractable surrogate on fixed data.

Yan-Sen Han, Shengyi Liao, Peng Sun et al. · 1 citation

#artificial intelligence Preprint Aug 2026

When Can Conditional Flow Matching Replace Pointwise Negative Log-Likelihood?

The decomposition provides a theoretical basis for adapting likelihood-based LLM methods to flow matching, while distinguishing exact substitutions from controlled surrogates, while distinguishing exact substitutions from controlled surrogates.

Yan-Sen Han, Hong-Xing Sun, Tao Lin · 1 citation