National Bank Open: Marta Kostyuk vs Katherine Sebov

Platform comparison

Market context

Marta Kostyuk against Katherine Sebov is a scheduled WTA National Bank Open match in Toronto, and in prediction markets a **YES** share means the named outcome happens, while a **NO** share means it does not. In this market, that means a YES pays out if Kostyuk advances over Sebov, and the market only goes to 50-50 if the match is not played, ends level, or is delayed beyond the settlement rules without a winner. [1][7][17]

The 100% crowd-implied probability points to a market that already prices Kostyuk as an overwhelming favourite, which fits the shape of the matchup. Kostyuk won the only recorded head-to-head meeting on hard court, beating Sebov in straight sets at Chicago in 2021, and the current rankings snapshot in the match listings places Kostyuk far higher than Sebov, who is shown as a wildcard entry. [2][3][7][15]

For traders, the main catalysts are practical rather than tactical: whether the match stays on the published schedule, whether Toronto’s draw or order of play changes, and whether any disruption pushes it outside the settlement window. Live match pages list the contest for 4 August at 15:00 UTC, but prediction markets can still reprice if there is a postponement, withdrawal, or an incomplete match that triggers the market’s special settlement rules. [1][8][11]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track National Bank Open: Marta Kostyuk vs Katherine Sebov across the five venues with material prediction-market liquidity. The probability shown is the live Polymarket mid; the comparison rows summarise how each venue treats the underlying contract — fees, KYC thresholds, settlement currency, deposit options. The highlighted row marks the cheapest route into Polymarket's order book.

Resolution & payout

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

FAQ

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is Prediction Market UK. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

Is this market available outside the US?

Polymarket itself is geo-blocked in the US/UK/EU. Always check the legal status of prediction markets in your jurisdiction before trading.

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

What's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Prediction Market UK trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.