Jaxformer is a JAX-based library for training large language models (LLMs) on TPUs with data and model parallelism. It provides a complete training loop supporting distributed training across TPU cores, checkpointing, and resumable data loading from TFRecord files. The codebase includes model definitions for transformer-based architectures (like CodeGen), utilities for learning rate scheduling and optimization, and integration with Hugging Face for model conversion and sampling. The system is designed for scalability, supporting models up to 6B parameters via sharding strategies, and includes tools for preprocessing large datasets into TFRecord format. While the core training functionality is tightly coupled to the TPU environment, several components like the resumable data iterator and checkpointing mechanism demonstrate reusable patterns.