U.S. prediction markets reach $1.3B open interest amid probes

Open interest across U.S. prediction markets reached $1.3 billion in April, up from $993.5 million in March. Kalshi held $636.4 million of the total, Polymarket held $589.8 million, and the remaining platforms together accounted for less than $25 million.

Kalshi reported a record $13.4 billion in spot volume in April, a 12.6% increase from March. Polymarket’s volume fell to $9.5 billion from $10.6 billion the prior month.

Legal and enforcement actions coincided with rising market activity. Federal prosecutors filed charges in a case alleging a U.S. Army Special Forces soldier used classified information about an operation involving Venezuela’s Nicolás Maduro to place bets on Polymarket and obtained about $410,000, according to authorities.

The U.S. Senate voted unanimously to bar members from participating in or trading on prediction markets. At the state level, a Nevada judge ordered Kalshi to geofence its site by May 4, blocking Nevada residents from accessing sports, election and entertainment contracts and finding the offerings indistinguishable from a sportsbook. Minnesota legislators advanced a bill that would make hosting prediction markets a felony.

An analysis of platform returns found 67% of Polymarket’s profits flowed to 0.1% of accounts, with fewer than 2,000 users capturing nearly $500 million. A separate review of active wallets since early 2025 identified more than 100,000 accounts that lost at least $1,000, almost double the number of accounts that posted comparable gains.

Investment and product developments continued alongside the legal actions. Kalshi’s valuation was adjusted to $22 billion. Polymarket raised $600 million with backing from Intercontinental Exchange. A decentralized exchange operator proposed adding prediction-market products, and the Commodity Futures Trading Commission closed a public comment period on a rulemaking to define regulatory boundaries for the sector.

Despite ongoing enforcement, rulemaking and court orders, open interest and capital inflows remained concentrated on the largest platforms. Operators, investors and regulators are responding with legal filings, legislation and proposed rules as market activity expands.