Arbitrage

Cross-platform arbitrage exploits the fact that Kalshi and Polymarket maintain separate Liquidity pools and participant bases, so prices for identical events frequently diverge. A trader monitoring both Order Book feeds looks for moments when the cost of buying YES on one platform plus the cost of buying NO on the other sums to less than $1.00. Because every binary contract pays exactly $1.00 at resolution, the difference between the combined cost and $1.00 represents gross profit. Trading Fees on each platform reduce net profit, so the price gap must exceed combined fees to be worthwhile. Automated bots using each platform Trading API are the dominant participants in this space because manual execution is too slow to capture fleeting gaps reliably.

Arbitrage in prediction markets carries several practical risks that distinguish it from the theoretical risk-free ideal. Execution risk arises because filling both legs simultaneously across two platforms is not possible, and prices can shift between the first and second fill. Slippage on a thin Order Book can erode or eliminate the spread. Resolution risk is particularly important: Resolution Criteria language may differ subtly between platforms, causing an event to resolve YES on one and also YES on the other, eliminating the hedge. Liquidity Risk limits position size when Depth of Market is shallow. Despite these constraints, arbitrage pressure is a healthy force in prediction markets, narrowing Bid-Ask Spread and keeping Implied Probability aligned with genuine market consensus.