How to Use PyTorch Lightning for LLM Training and Fine-Tuning
A practical guide to PyTorch Lightning for ML engineers working on LLMs: LightningModule structure for fine-tuning, LightningDataModule for reproducible data pipelines, Trainer configuration for multi-GPU with FSDP and mixed precision, LoRA fine-tuning with PEFT integration, gradient accumulation and checkpointing, and a clear-eyed comparison of when Lightning helps versus when Accelerate or raw PyTorch DDP is the better choice.