River AI Raises $1.1B Two Months After Exiting Stealth

River AI raised $1.1 billion in a seed/Series A round led by General Catalyst and AMP PBC, with Nvidia, AMD Ventures, Y Combinator, and Temasek participating. Founded by xAI co-founder Igor Babuschkin (ex-DeepMind, OpenAI), the company emerged from stealth in June 2026 and is building an open AI stack for reinforcement learning and LoRA fine-tuning on open models via a live API.