National Bank Open: Marta Kostyuk vs Katherine Sebov

Platform comparison

Market context

Polymarket is pricing **Marta Kostyuk** at **100% YES** and **Katherine Sebov** at effectively zero in this contract, so the market is behaving as if the outcome is already locked in on-chain. On Polymarket, that means traders are holding USDC-settled, Polygon-based conditional tokens whose final value depends on the official match result rather than the pre-match narrative.

That reading fits the wider tennis context: Kostyuk is a significantly higher-ranked player, and several match-preview and odds pages also lean heavily towards her, with implied win chances around the low-to-mid 90s and a straight-sets expectation in some previews.[1][7][13][14] The head-to-head data shown in live tennis listings also points to Kostyuk leading Sebov 1–0, which is consistent with a one-sided price.[9][15]

The main thing traders should watch is whether the match is actually played and finished within the settlement window, because this contract can still resolve to 50-50 if it is cancelled, ends level, or is delayed beyond seven days without a winner. Official tournament results pages, live scoreboards, and any schedule changes from the National Bank Open are the key dependencies, since a walkover, retirement after the match starts, or a rescheduling issue can matter more here than the pre-match odds.[2][10][12]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

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

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 PolyGram. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

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.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

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.