Kalshi overtakes Polymarket as October trading surges

Prediction markets recorded their busiest month to date in October, with Kalshi trading more volume than Polymarket for the first time in a single month. Kalshi logged $4.39 billion in October trading volume, while Polymarket’s monthly volume rebounded to $3.02 billion and its active-trader count reached a record 477,850.

Polymarket’s active-trader total was 93.7% higher than September’s 246,610 and surpassed its previous high of 462,600, set in January. The platform listed 38,270 new markets during October, nearly three times its August count.

Polymarket’s monthly volume had remained below $1 billion from February through August. Its October recovery was linked by Startup Fortune to preparations for a U.S. relaunch, speculation about a possible POLY token, and trading strategies involving liquidity provision, arbitrage and information asymmetry.

Kalshi’s activity accelerated sharply in the week of Oct. 5-11, when contract volume reached a company-record $19.03 billion. It set consecutive daily records of $3.91 billion on Oct. 10 and $3.96 billion on Oct. 11, with parlay-style combo contracts accounting for about 70% of the week’s activity.

The figures extend the football-driven weekly surge at Kalshi and Polymarket, as we reported Oct. 11, when the two venues reached a combined record $22.2 billion week.

The different volume tallies should not be treated as directly comparable. Pew Research Center’s measure of Kalshi and Polymarket activity counts notional taker volume, valuing every contract at $1 rather than its transaction price. On that basis, the platforms’ combined monthly volume rose from $26 billion in May to $53 billion in July, largely because of sports trading, before easing to $47 billion in August. Kalshi and Polymarket had each represented about half of prediction-market volume as recently as March, Pew found, before Kalshi grew more quickly.

The rapid expansion has also drawn questions about the quality of reported activity. CNBC cited a Columbia University study that classified patterns indicative of wash trading as 60% of Polymarket International’s weekly volume in December 2024 and 20% in October 2025, although the study’s lead author said the measure had fallen to a negligible level by April. The Commodity Futures Trading Commission’s chairman, Michael Selig, said the agency had zero tolerance for manipulative trading, including wash trading, insider trading and fraud.

The growth has heightened investor interest. Kalshi was discussing a roughly $1 billion fundraising round at a $40 billion valuation, with Sequoia Capital and Wellington Management in talks to lead and Tiger Global and Dragoneer considering participation. Kalshi had closed a $1 billion Series F in May at a $22 billion valuation. Polymarket, meanwhile, was negotiating a round at about a $15 billion valuation, while Intercontinental Exchange had invested as part of a plan to put as much as $2 billion into the company.

Regulatory disputes continue alongside the expansion. Kalshi Klear filed a Sept. 22 request with the CFTC to permit some institutional traders to buy event contracts on margin. A Massachusetts court blocked Kalshi’s sports markets in the state after ruling in January that it was operating as an unlicensed sportsbook, and Kentucky sued both Kalshi and Polymarket over allegations that they operated without gaming licences.