The Allen Institute for AI has released OLMo, a truly open large language model, along with its pre-training data and training code. This release aims to provide the industry with an opportunity to understand how AI models are created and to advance the science of language models collectively. OLMo is designed to aid researchers in training and experimenting with large language models, and it is available for direct download on Hugging Face and GitHub. The model is built on Ai2's Dolma set, which features a three trillion token open corpus for language model pretraining.