Monthly U.S. prediction market volume rises as accuracy and insider-trading scrutiny intensify
Prediction market platforms Polymarket and Kalshi attracted millions of dollars in wagers during the 2026 midterm cycle, according to reports from November 15. The activity has generated allegations of insider trading on both platforms.
The millions in wagers pouring in during an election cycle make insider-trading allegations harder to dismiss as edge cases. When anonymous users can bet on political outcomes, any trader with non-public information has a direct financial incentive to exploit it. Polymarket and Kalshi, the platforms now face parallel pressure to prove either that their controls catch misconduct or that their crowdsourced pricing is accurate enough to justify the risk. Kalshi's monthly volume lead in November shows it is gaining ground on Polymarket's dominant annual share.
That competition for users amplifies the stakes: whichever platform looks softer on manipulation could lose the traders driving that growth. Senators Warren and Curtis have already demanded internal trading data under bipartisan deadline. Any fresh evidence of suspicious trades by cleared personnel feeds directly into their investigation and gives state attorneys general a template for arguing these markets are gambling venues that privilege connected insiders.
Adds a third dimension to the running post-election reform push affecting Kalshi and Polymarket, after congressional demands for internal trading data and a state-by-state legal assault on their federal preemption shields.