The Allen Institute for AI (AI2) has released Tülu 3, a groundbreaking open-source post-training framework aimed at democratizing advanced AI model development. This comprehensive suite includes state-of-the-art models, training datasets, code, and evaluation tools, enabling researchers and developers to create high-performance AI models rivaling those of leading closed-source systems. Tülu 3 introduces innovative techniques such as Reinforcement Learning with Verifiable Rewards (RLVR) and extensive guidance on data curation and recipe design. By closing the performance gap between open and closed fine-tuning recipes, Tülu 3 empowers the AI community to explore new post-training approaches and customize models for specific use cases without compromising core capabilities.