Problem

Professional traders and hedge funds currently face an infrastructure problem when trading prediction markets. Retail-oriented platforms force them to juggle browser tabs, place and manage orders venue by venue, and manually monitor fills, diverting time from research and trading strategy to operations. Liquidity is fragmented because identical event contracts can trade at different prices across exchanges, while constantly changing APIs make systematic trading expensive to maintain.

The main use case is a fund or professional trader running strategies across multiple prediction-market venues. River’s value proposition is therefore both economic and operational: better execution on the same contracts, less slippage and manual work, and fewer engineering resources spent maintaining exchange connectors. River says its smart routing can improve pricing by up to 50%, while its website cites roughly two cents of average price improvement.

Product / Service

River Markets provides a prime-brokerage and execution layer for prediction markets. It aggregates trading across Kalshi, Polymarket, Polymarket US, and other venues into one account and terminal, with a multi-book interface for placing, modifying, and cancelling hundreds of orders. The platform includes a unified order-management system, cross-venue smart routing, baskets, subaccounts, position and P&L views, and server-managed order types such as icebergs, pegs, take-profits, and stop-losses.

For systematic traders, River offers an institutional-oriented API with a standardized contract identifier, REST and WebSocket access, real-time order-book and trade streams, and an official Python SDK. Traders integrate once rather than building and maintaining a separate connector for each exchange; River handles execution, routing, settlement, and P&L across venues. The benefit is a single operating layer for prediction-market trading rather than a collection of disconnected retail accounts and custom integrations.

Market

River competes in the emerging institutional prediction-market brokerage, execution, and trading-infrastructure category. Its underlying venues include Kalshi, Polymarket, Polymarket US, and Novig, but River positions itself as the layer that connects and optimizes access to those markets rather than as another event-contract exchange. The broader market is expanding quickly: Finadium reported monthly prediction-market volumes of $20 billion in March 2026 and described the sector as approaching institutional adoption, while also noting unresolved questions around regulation, margin, settlement, and technology integration.

The closest evidenced adjacent competitor is Dome, a unified prediction-market API for accessing, analyzing, and trading across platforms, although Y Combinator lists Dome as inactive. The larger alternative is for professional traders to build their own venue integrations or rely on traditional prime brokers that have not yet fully adapted to prediction markets. River is not pre-product: at its May 2026 YC launch it reported more than $50 million traded, 200% week-over-week growth since early April, usage by three of the top ten traders on Kalshi and Polymarket, and several quant funds using its API. Revenue, pricing, and audited trading figures were not disclosed.