Originally published on AI Tech Connect.
What you need to know $1.1B across seed and Series A, announced 11 August 2026, led by General Catalyst and AMP PBC. Nvidia, AMD Ventures, Temasek and Y Combinator participated. The seed/Series A split was not disclosed. The company is under four months old from incorporation, and two months out of stealth. River AI was incorporated in April 2026 and came out of stealth in June. River declined to disclose a valuation; several outlets reported a figure of roughly $5B post-money, which River has not confirmed. The product is an own-your-weights stack: an API for LoRA fine-tuning and reinforcement learning on open-weight models, so the customer ends up owning the resulting model rather than renting someone else's. The builder question is not "is this real" — it is whether owning weights now…
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