River's mission is to democratize powerful AI. We believe that each individual and each company should be able to easily train and serve their own models, specially tailored to their needs. Before River, large-scale fine-tuning and reinforcement learning (RL) required a massive, dedicated AI infrastructure team and expensive hardware. River changes that. The River API delivers state-of-the-art LoRA fine-tuning and reinforcement learning for frontier open-source models (Qwen, GLM, Kimi) ranging from 35B to 1T parameters.