Structural Arbitrage

In a prediction market where exactly one team wins, buying every possible outcome for $1.00 total should be a break-even trade — you're guaranteed to hold the winning share, which pays exactly $1.00 at settlement. When you can buy every outcome for less than a dollar, the trade becomes risk-free profit. No opinion on the game required. No edge needed on who wins. The math guarantees the return. Structural Arbitrage is the engine that finds these moments and executes before they close.

// WHY PRICES BREAK

Polymarket uses a structure called NegRisk for its binary sports markets — markets where exactly one outcome resolves to $1.00 and all others go to zero. In theory, if you add up the prices of every outcome in a NegRisk group, the sum should equal $1.00. In practice, it often doesn't.

Different participants trade different outcomes independently. A trader who thinks Team A is underpriced buys YES on Team A without necessarily considering what that implies about the price of Team B or Team C. A market maker updates their quotes in one market but not the linked ones fast enough. News hits, one outcome reprices immediately, the others lag. The result is that the sum of all outcome prices drifts — sometimes above $1.00, sometimes below.

Both directions are tradeable. When the sum falls below $1.00 — buy every outcome and collect the difference at settlement. When the sum rises above $1.00 — sell every outcome and collect the overage. The second version requires minting a complete set of outcome shares at $1.00 and selling each one above its fair share of that dollar, but the logic is the same.

// HOW IT RUNS

The engine scans every active NegRisk market group every 500 milliseconds. When it finds a discrepancy large enough to clear the 2% Polymarket fee and estimated gas costs — in practice, a total cost below about $0.975 to buy all outcomes, or total proceeds above about $1.025 to sell all — it triggers an execution within 200 milliseconds of detection.

Every leg of the trade is placed simultaneously using fill-or-kill orders. Fill-or-kill means the order either fills completely or is cancelled immediately — no partial fills. This matters because structural arb only works when all legs fill. If you buy Team A's YES shares but fail to buy Team B's, you now have a directional position with no intentional edge. If any leg rejects, all other legs are cancelled instantly.

These windows are brief. Arbitrage scanners — including competing bots — close them fast. When an opportunity is detected, Matchpoly prioritizes it above every other strategy type, submits all legs at the same instant, and settles at resolution without any active management needed. The profit is locked at entry.

Beyond the basic price-sum check, the engine also tracks logical relationships between linked markets. A market for "Conference champion" and a market for "League champion" from the same team are mathematically related — the conference winner's odds to win the league should never exceed their conference championship odds. When a logical impossibility appears across linked markets, that's a tradeable discrepancy too.

See also: Risk Management · The Pinnacle Gap