Title: Sharpness-Aware Minimization in Large-Batch Training: Training Vision Transformer In Minutes. Abstract: Large-batch training is an important direction for distributed machine learning, which can improve the utilization of large-scale clusters and therefore accelerate the training process. However, recent work illustrates that large-batch training is prone to converge to sharp minima and cause a huge generalization gap. Sharpness-Aware Minimization (SAM) tries to narrow the generalization gap by seeking parameters that lie in a flat region. However, it requires two sequential gradient calculations that doubles the computational overhead. In this paper, we propose a novel algorithm LookSAM to significantly reduce its additional training cost. We further propose a layer-wise modification for adapting LookSAM to the large-batch training setting (Look-LayerSAM). Equipped with our enhanced training algorithm, we are the first to successfully scale up the batch size when training Vision Transformers (ViTs). With a 64k batch size, we are able to train ViTs from scratch within an hour while maintaining competitive performance.