River AI Raises $1.1 Billion Two Months After Exiting Stealth

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