Polymarket has deeper liquidity (~$50M+ across major markets) and wider coverage including international politics and crypto. Kalshi is CFTC-regulated US-only with strong domestic political and economic markets. For sharp traders, Polymarket's lower vig and greater liquidity usually win.

Polymarket has far more liquidity and no position cap. PredictIt survived its court fight (Clarke v. CFTC, July 2025) and its per-contract position limit was raised to $3,500 under the July 2025 CFTC settlement, but it still operates under an amended CFTC no-action letter (not as a registered exchange), charges a 10% fee on profits plus a 5% withdrawal fee, and is limited to US politics. As of 2026, Polymarket is the better choice for serious traders.

Lower vig (2–5% vs 7–10%), no winner limits, trade-out flexibility, and on-chain transparency. Sportsbooks cap or ban consistent winners; prediction markets don't.