Arbitrage between prediction markets Polymarket and Opinion is quite common right now. The more similar the prediction events, the more potential arbitrage opportunities there are. Opinion has some markets that directly mirror or are highly similar to Polymarket, such as events related to the Federal Reserve's interest rate decisions and crypto price predictions. Overlapping event predictions often present arbitrage opportunities. Opinion and Polymarket currently differ in user base, liquidity, and speed of information dissemination. These differences often lead to price discrepancies when predicting the same event. For example, Opinion leans more toward DeFi users, while Polymarket is more global, attracting some non-crypto users. Different user perspectives contribute to price deviations. The classic arbitrage method is to buy Yes on one platform (Polymarket or Opinion) and buy No on the other, resulting in a total cost < 1, allowing for risk-free profit upon settlement. Arbitrage players are very active right now, using multiple specialized tools and scanners to monitor price discrepancies across Opinion, Polymarket, and Kalshi in real time. Some tools, like PredAlpha (which specifically compares Polymarket and Opinion's real-time prices to identify arbitrage opportunities), Polyar, and GetArbitrageBets, also support multi-platform real-time arbitrage scanning, alerts, and APIs for Opinion, Polymarket, and Kalshi. However, manual arbitrage players (mostly retail traders) find it more challenging (small-scale opportunities exist). Currently, most arbitrage is dominated by high-frequency bots, with opportunities typically lasting only a few seconds or minutes. Especially for high-liquidity events (like trending topics), prices are becoming increasingly similar, and the arbitrage window is very short (seconds-level).