Kalshi has become the exclusive prediction market partner of the US Open under a deal with the United States Tennis Association that took effect as the main draw began in New York. The arrangement was completed after the tournament’s qualifying rounds and covers the 2026 event, according to people familiar with the matter.

Financial terms were not disclosed. The partnership places Kalshi in an official role at one of tennis’s four Grand Slam tournaments and restricts competing prediction market platforms from advertising at the Flushing Meadows venue and across television coverage, including ESPN broadcasts.

Last-Minute Agreement Driven by New Leadership

The USTA had previously considered waiting until 2027 or later before entering any prediction market partnership. Discussions in recent weeks involved multiple platforms and focused in part on match integrity. Plans shifted after Craig Tiley assumed the role of USTA chief executive on July 20. Tiley, who previously spent 21 years leading Tennis Australia, played a central part in advancing an agreement for the current tournament.

The deal’s timing left little room for public rollout. When the main draw started, Kalshi did not appear on the US Open’s official partner list. A Kalshi analysis of the women’s singles field published the same day still carried a disclaimer stating the company was not affiliated with the US Open or the WTA. Neither Kalshi, the USTA, nor ESPN had issued a formal public confirmation at the time the main draw opened.

Active Markets and Broader Sports Push

Kalshi already listed numerous contracts linked to US Open matches. Individual men’s and women’s singles markets saw significant activity, with some contracts exceeding $1 million in trading volume. The women’s singles tournament winner market alone had drawn roughly $1.6 million in volume by early Monday.

The US Open agreement continues Kalshi’s expansion into major sports properties. In late August the company announced partnerships with five Major League Baseball clubs: the Atlanta Braves, Boston Red Sox, Los Angeles Dodgers, San Diego Padres and San Francisco Giants. Baseball-related trading volume on the platform has risen approximately 36-fold year over year. Kalshi also holds a shared NHL relationship and previously secured World Cup branding exposure through an arrangement with FIFA’s official prediction market partner.

Sports contracts have become a primary driver of activity for the platform. Weekly trading volume reached a record $5.1 billion in June during the World Cup period, with sports-related contracts forming its largest product category. Across the wider sector, Kalshi, Polymarket and related platforms generated substantial combined volume in August, with Kalshi accounting for the majority of that activity.

Regulatory Uncertainty Persists

The commercial expansion is unfolding against an unsettled legal backdrop. On August 28 the Ninth U.S. Circuit Court of Appeals ruled that Kalshi had not shown the Commodity Exchange Act was likely to preempt Nevada gaming regulations as applied to its sports event contracts. The panel affirmed in part a lower-court order dissolving a preliminary injunction that had blocked Nevada enforcement.

Nevada regulators had earlier directed Kalshi to cease operations they viewed as unlicensed sports betting. Kalshi maintains it operates as a designated contract market under federal commodities law and that the Commodity Futures Trading Commission holds exclusive authority over its event contracts. The Ninth Circuit found the sports contracts at issue did not qualify as swaps under the relevant statutory definition.

That outcome conflicts with a prior Third Circuit decision that upheld preliminary relief blocking New Jersey regulators from enforcing state gambling laws against Kalshi’s sports contracts. A federal judge in New York has also rejected Kalshi’s bid for an injunction, allowing state claims to proceed. Additional pressure arrived in mid-August when Baltimore filed suit against Kalshi and Polymarket, alleging unlicensed sports betting and seeking penalties, restitution and an order barring the platforms from offering such contracts to city residents.

Kalshi has developed internal compliance measures for sports markets, including screening systems intended to identify athletes, coaches, referees and league personnel prohibited from trading certain contracts. Those tools operate alongside proprietary detection engines and third-party surveillance platforms. The company continues to argue that its federal regulatory status permits the contracts it lists, even as state and local challenges multiply.

The US Open partnership underscores the growing interest of major sports organizations in prediction markets while highlighting the unresolved jurisdictional questions that still surround the product category.