Polymarket arbitrage scanner — and Kalshi price gaps.

In a mutually exclusive event, exactly one outcome pays $1. If the best asks for YES on every outcome add up to less than $1, buying all of them locks in the difference. If the best bids add up to more than $1, selling them all does. The scanner checks this across the busiest multi-outcome events, after Polymarket’s taker fees.

Rarely, and they close fast — Polymarket’s books mostly add up. The scanner shows any live gap first and the closest near-misses below, so you can watch where one might open.

Cleus matches Polymarket events to the same proposition on Kalshi and shows both prices side by side. Gaps of a few points appear in the terminal’s Price gaps view. Remember the venues have different fees, rules wording and settlement — read both before treating it as arbitrage.

For crypto price markets (“Bitcoin above $X on date”), Cleus prices the same outcome from Deribit options’ implied volatility — no AI involved. Where Polymarket is far from it, the gap is objective. Options usually price in a little more movement than happens, so they lean high on long shots.

Yes, the scanner and price gaps are free.