The Development of Sycophancy in Language Models: Tracing Vulnerabilities from Pretraining to Post-Training

Haonan Huang, Chengkun Cai · 2026 · arXiv

DOI: 10.48550/arXiv.2610.26655 · open-access PDF

Abstract

Language models can change a committed answer to accommodate a user's opinion or pushback without new evidence. However, when this behaviour develops during training and what a released model inherits from earlier stages remain unclear. We follow 741 checkpoints of 30 open model lineages, from early pretraining to released models. We plant initial verdicts on moral scenarios and measure how far a model follows a user's stated opinion or abandons its verdict under pressure. In most lineages the behaviour is present before post-training, and its average strength changes in either direction, at d

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