Infiniti Briefing

Kalshi accounted for 75.6% of tracked prediction-market trading volume in the 30 days to October 7, according to a DataWallet comparison citing DeFi Rate data. Polymarket US represented 11.6%, while Polymarket’s international platform accounted for 5.3%. Kalshi also had $2.5 billion in open interest on October 7.

Scale comes with a measurement caveat

DataWallet’s comparison, last updated October 10, 2026, says its figures were verified on October 9, 2026. It reports that September 2026 set monthly records for Kalshi, with $60.7 billion in trading, and Polymarket US, with $8.8 billion. Polymarket’s international platform recorded $4.5 billion over the 30 days to October 7 and had $339 million in open interest.

Those trading totals do not measure the dollars traders actually paid. According to DataWallet, the data providers value each traded contract at its $1 potential payout. Across all tracked platforms, reported volume of $89.4 billion corresponded to $23.4 billion paid. Open interest is a separate measure: the value of contracts still awaiting settlement.

Sports dominate, but political depth differs

Sports and multi-event positions account for much of the activity behind the headline shares. DataWallet reports that combos represented 64.3% of Kalshi’s volume in the week ending October 4, with single sports contracts contributing about 19.8%. Sports generated 98.4% of Polymarket US volume in the 30 days to October 7 and 46.2% of recent activity on its international platform.

The ranking differs in politics. Citing Pew Research Center, DataWallet reports that Polymarket recorded $1.3 billion in political trading in June 2026, compared with $261 million for Kalshi. The comparison describes Polymarket’s political markets as deeper, underscoring that overall platform volume and liquidity in a particular category are not interchangeable.

What it means for prediction markets

• The lead is in tracked volume. Kalshi’s 75.6% share applies to the stated 30-day window and dataset, rather than every possible measure of platform activity.
• Volume is not cash committed. Payout-based turnover and open interest describe different aspects of trading; neither should be substituted for the amount traders paid.
• Category mix matters. Sports-heavy activity helps explain the aggregate rankings, while the cited political-market figures favor Polymarket.
• The snapshot has a cutoff. The comparison was updated October 10, 2026, but the headline volume window and open-interest figures end on October 7.