River Markets, a prediction-market trading infrastructure startup, has raised $8.5 million in a seed round led by Haun Ventures that closed in July, with participation from Y Combinator, Coinbase Ventures and Qube Research Technologies, which earlier reporting identified as Cube Research Technologies. The San Francisco-based company launched in May and is positioning itself as a prime-brokerage layer for event contracts, giving hedge funds and proprietary trading firms a single account to access Kalshi, Polymarket, Polymarket US and Novig. Its platform offers smart order routing, iceberg orders, advanced order types and unified portfolio management across venues in a market where institutions otherwise need separate accounts, workflows and risk tools for each exchange. River Markets says it has facilitated more than $50 million in trading volume and supports three of the top 10 traders on both Kalshi and Polymarket. The company argues that demand is rising as firms use prediction markets for hedging and event-driven trades, with Kalshi operating under CFTC regulation and Polymarket relying on Polygon-based, on-chain settlement that drew heavy activity during the 2024 U.S. presidential election cycle. CEO Oscar Levy and CTO Antonin Parrot said the funding will help River Markets add engineers, improve the speed and security of its system and expand tools for larger-scale institutional trading.