A Flexible Vision Transformer is a deep learning architecture designed to process and generate visual content across unrestricted resolutions and arbitrary aspect ratios by representing images as dynamically sized sequences of tokens rather than rigid, fixed-resolution grids. Unlike traditional vision transformers that constrain inputs to uniform dimensions through standard cropping and resizing, this framework adjusts to varying sequence lengths during both training and inference phases. This structural flexibility mitigates cropping-induced biases, supports seamless adaptation to diverse aspect ratios, and facilitates resolution generalization and extrapolation, particularly within generative modeling frameworks such as diffusion transformers.