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arXiv · 2510.17426

Navigating the Alignment-Calibration Trade-off: A Pareto-Superior Frontier via Model Merging

Tiancheng Hu·Benjamin Minixhofer·Nigel Collier
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Abstract

The "alignment tax" of post-training is typically framed as a drop in task accuracy. We show it also involves a severe loss of calibration, making models overconfident, less reliable, and model outputs less diverse. We show that this trade-off can be navigated effectively via a simple post-hoc intervention: interpolating between a model's weights before and after alignment. Crucially, this is not a strict trade-off. We find that the process consistently reveals Pareto-optimal interpolations - models that improve accuracy beyond both parents while substantially recovering the calibration lost during alignment. Our work demonstrates that simple model merging provides a computationally efficient method for mitigating the full scope of the alignment tax, yielding models that are more capable and more reliable.

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Tiancheng Hu, Benjamin Minixhofer, Nigel Collier. 2025-10-20. Navigating the Alignment-Calibration Trade-off: A Pareto-Superior Frontier via Model Merging. https://arxiv.org/abs/2510.17426

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