Kalshi vs. Polymarket: Who Decides Winners and When Funds Can Leave

Prediction‑market giants Kalabi and Polymarket have become the focus of a showdown over who determines market winners and when traders can withdraw funds. The dispute erupted after reality‑TV spoilers on shows such as Survivor 50 were traced to massive wagers on Kalabi, where a user’s $45,500 bet on Aubrey Bracco turned a $4,500 profit, and on Polymarket, where similar odds emerged. CBS host Jeff Probst publicly criticized the platforms on October 31, 2026, prompting Kalabi to announce new anti‑spoiler features while both firms defended their surveillance practices. The controversy coincides with the NBA’s new partnership with the two platforms, raising questions about market integrity and regulatory oversight.

Background

Kalabi and Polymarket operate as CFTC‑designated contract markets, allowing traders to buy and sell contracts that settle at $1 if a predicted outcome occurs and $0 otherwise. Their fee structures differ, with Kalabi using a maker‑taker model and Polymarket applying probability‑weighted taker fees that vary by category. Both platforms have attracted massive volumes in 2026, especially in sports markets driven by the World Cup. Beyond sports, they host cultural and political contracts, including reality‑TV outcomes. The CFTC regulates these markets, distinguishing them from offshore prediction sites and traditional sportsbooks. However, state regulators in New York, New Jersey and elsewhere have challenged the legality of such contracts, alleging they constitute illegal sports betting. The NBA recently signed an integrity framework with Kalabi and Polymarket, granting the league input on market offerings and sharing data with the CFTC. Meanwhile, the IRS has not clarified the tax treatment of event contracts, leaving traders uncertain about the applicability of the Section 1256 60/40 rule. This regulatory backdrop frames the current debate over market winner determination and fund withdrawal policies.

What happened

When the Survivor 50 market opened on Kalabi six weeks before the February 25 season premiere, traders quickly pushed Aubrey Bracco’s implied probability to 61%, later rising to 83% by January 28 and 97% by the finale, with $32.7 million in wagers recorded (Source 1). A single user placed a $45,500 bet on Bracco shortly after the premiere, earning a $4,500 profit (Source 1). Polymarket saw $1.9 million in volume on the same market, with odds following a similar trajectory (Source 1). Kalabi’s head of communications, Elisabeth Diana, said the platform uses AI‑powered third‑party surveillance to flag suspicious trades, and head of enforcement Robert DeNault posted on X that no large‑position traders appear linked to the show (Source 1). Polymarket declined to comment (Source 1). On the same day, Jeff Probst criticized the platforms for encouraging dishonest behavior, prompting Kalabi to issue a statement about adding spoiler‑prevention features (Source 1). Separately, Fox Sports outlined the fee and market differences between Kalabi and Polymarket, noting both are CFTC‑regulated and that sports now dominate their 2026 volume (Source 2). The NBA announced a partnership with both platforms, establishing an integrity framework and sharing information with the CFTC, while acknowledging ongoing state legal challenges (Source 4, Source 5). The IRS has not provided guidance on whether event contracts qualify for the Section 1256 tax break, leaving traders in a gray area (Source 3).

Market impact

Kalabi’s Survivor 50 market attracted $32.7 million in wagers, pushing Bracco’s odds to 97% by the finale, while Polymarket’s version saw $1.9 million in volume with similar odds movement (Source 1). A single Kalabi user’s $45,500 bet yielded a $4,500 profit (Source 1). In sports categories, the World Cup drove record volume on both platforms in 2026, though exact figures were not disclosed (Source 2). Kalabi’s fee model includes a per‑contract taker fee that peaks near 50‑cent contracts and a 2 percent debit‑card deposit fee, while Polymarket applies a probability‑weighted taker fee that is highest around 50 percent priced contracts (Source 2). Both platforms charge no deposit or withdrawal fees for most funding methods, meaning cost differences hinge on contract type and funding choice (Source 2). The NBA partnership may expand market liquidity by granting access to official league data and branding, though specific financial impacts remain speculative (Source 4, Source 5).

Why it matters

The ability of traders to predict reality‑TV outcomes with high accuracy raises concerns about insider information and market manipulation, prompting platforms to bolster surveillance and consider new anti‑spoiler tools (Source 1). The NBA’s partnership signals mainstream acceptance of prediction markets, yet it also places leagues in the crosshairs of state regulators who argue such contracts amount to illegal betting (Source 4, Source 5). The CFTC’s regulatory role differentiates these markets from traditional sportsbooks, but ongoing lawsuits by states and pending Supreme Court decisions could reshape the legal landscape (Source 4, Source 5). Tax uncertainty surrounding event contracts adds another layer of risk for traders, as the IRS has not clarified whether the Section 1256 60/40 rule applies, potentially affecting after‑tax returns (Source 3). Together, these factors influence how winners are determined, when funds can be withdrawn, and the broader credibility and growth prospects of the prediction‑market industry.