National Bank Open: Marta Kostyuk vs Katherine Sebov

Platform comparison

Market context

Marta Kostyuk and Katherine Sebov were scheduled to meet in the National Bank Open second round, and the market has settled into a near-certainty profile because the live and results feeds show the match was already underway and had moved into a decisive position rather than sitting as a fresh pre-match event.[4][15] The crowd-implied 100% YES reflects that the market is no longer pricing a normal pre-match uncertainty band; it is effectively tracking the on-court state, with Kostyuk listed as the higher-ranked player at world No. 11 and Sebov as the wildcard ranked No. 231.[3][7]

The historical frame is straightforward: their only previous meeting was won by Kostyuk in straight sets at Chicago in 2021, 6-0, 6-3, and the official match notes still list her as leading the head-to-head 1-0.[2][9] That is the main comparable case for reading this market, because it points to a consistent ranking and quality gap rather than a rivalry with swingy outcomes, although one prior meeting is still a thin sample.[2][9]

What traders should watch now is not form in the abstract but whether the tournament and live score services continue to report a completed result without interruption, because the settlement rules only fall back to 50-50 if the match is cancelled, tied, or delayed beyond seven days.[4] The key dependencies are the official National Bank Open results page, which already carries full match statistics, and the live scoring feeds, which are the fastest indicators of whether the result has been finalised or whether an administrative delay could force a different resolution.[4][6][15]

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

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

FAQ

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 Today trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.