River AI raises $1.1B at $5B valuation, ex-xAI co-founder Igor Babuschkin

River AI, founded two months ago by ex-xAI co-founder Igor Babuschkin, raised $1.1B at a ~$5B valuation, co-led by General Catalyst and AMP PBC with NVIDIA, AMD Ventures, Temasek and Y Combinator participating. The company offers an API for LoRA fine-tuning and RL on frontier open-weight models from 35B to 1T parameters.