"Risk-free" is a strong claim. In practice, pure arbitrage on prediction markets is about as close as retail traders get to truly risk-free returns — but there are real risks that anyone running an arbitrage strategy needs to understand and manage.
What arbitrage actually is
In theory, buying both sides of a binary contract for a combined cost below $1.00 guarantees a $1.00 payout. The profit is locked in regardless of whether YES or NO wins. This is the textbook definition of risk-free arbitrage.
In practice, the word "risk-free" requires three conditions to be met: both legs must fill at the quoted prices, the contracts must resolve as expected, and fees must not eliminate the edge. All three have failure modes.
The real risks
Leg fill risk. You place your YES order on Polymarket and it fills. Then you go to place your NO order on Kalshi — but the price has moved and the spread has closed. Now you're holding a directional YES position with no hedge. This is the primary operational risk in prediction market arbitrage. Mitigation: execute both legs near-simultaneously using automation; set a tight timeout and exit Leg 1 if Leg 2 doesn't fill.
Resolution risk. Prediction markets occasionally resolve controversially or incorrectly. A contract might resolve NO even though most traders expected YES, due to ambiguous wording or disputed facts. This is rare but real. Mitigation: read contract resolution criteria carefully; avoid contracts with ambiguous or subjective resolution conditions.
Liquidity risk. You identify an arbitrage opportunity but can't fill the desired size at the quoted price because the order book is too thin. Your actual average fill price eliminates the edge. Mitigation: always check order book depth before committing to a size; use limit orders.
Fee drag. Platform fees on both sides can eat all or most of a thin edge. Mitigation: model fees explicitly; set a minimum net edge threshold (typically 1.5%+) before trading.
Platform risk. Smart contract bugs (Polymarket), regulatory action (Kalshi), or platform insolvency. Low probability but non-zero. Mitigation: don't hold large balances on-platform between trades; diversify across venues when possible.
How to mitigate each risk
Arbitrage Agent handles the three main operational risks automatically: simultaneous dual-leg execution (minimises leg risk), order book depth checking before submission (minimises liquidity risk), and explicit fee modelling in edge calculations (eliminates fee-drag errors). Resolution and platform risk remain the trader's responsibility.
Why it's still the closest thing to risk-free
Compared to directional trading — where you're betting on an uncertain future outcome — pure arbitrage has dramatically lower risk. The expected value calculation doesn't depend on predicting anything. You're capturing a mathematical certainty, constrained only by execution quality. Join the waitlist to get automated access to these opportunities.