River Markets, a San Francisco-based prime brokerage for prediction markets, has raised $8.5M in seed funding led by Haun Ventures. The platform provides hedge funds, prop trading firms, and professional traders with a unified terminal and API for trading across venues including Kalshi, Polymarket, and Polymarket US, handling smart order routing, normalized data, and execution algorithms like Icebergs and Pegs. The capital will support engineering expansion and operational scaling.
Prediction Markets Draw Institutional Capital
The timing aligns with explosive volume growth in prediction markets. Kalshi raised $1B+ at a $22B valuation in March 2026, while Polymarket secured $600M at ~$9B valuation in October 2025. River Markets differentiates by aggregating liquidity across venues rather than operating as an exchange itself.
Fragmented Venues Create Execution Inefficiency
Professional traders currently manage separate accounts, APIs, and risk systems across multiple platforms, leading to suboptimal pricing and operational overhead. Research from River Markets highlights a hidden 2.4% tax on trades due to naive execution, with smart routing delivering average price improvements of 2 cents per contract.
Unified Platform Replaces Multi-Venue Workflows
River Markets aggregates order books from all major venues into a single interface, offering cross-venue smart routing, server-side execution algorithms, and unified P&L attribution. This approach contrasts with venue-specific tools from Kalshi or Polymarket and generalist prime brokers that lack prediction-market-native features.
"This transition from mainstream retail to institutional can't really be achieved with today's consumer interfaces," noted CEO Oscar Levy.
The platform already serves several of the top 10 traders by volume on Kalshi and Polymarket.
Haun Ventures Leads Strategic Investor Syndicate
Haun Ventures led the round with participation from Y Combinator, Coinbase Ventures, Qube Research & Technologies, and angels from Citadel, Google, HRT, and JPMorgan. The syndicate reflects conviction in prediction markets as an emerging asset class that requires dedicated infrastructure.
Volumes Surge Toward Trillion-Dollar Scale
Annual volumes reached an estimated $240B in 2026 and are projected to hit $1T by 2030, according to Bernstein. Monthly volumes grew from $1.2B in early 2025 to over $20B by January 2026. This growth is driving demand for professional-grade execution tools that traditional prime brokers are only beginning to address.
Quant Founders Build From Trading Experience
Founders Oscar Levy, formerly a BlackRock VP managing $6B portfolios, and Antonin Parrot, an ex-HFT options market maker, launched the company in April 2026 after developing the software as a side project that generated seven figures in profits. The team started with real users on day one.