National Bank Open: Marta Kostyuk vs Madison Keys

Platform comparison

Market context

Marta Kostyuk and Madison Keys are the underlying WTA match here, and the market is priced as though Keys remains a very strong favourite, with the crowd-implied 97% YES sitting near the “Keys advances” side of the contract. That looks high against the historical match-up: Keys leads the head-to-head 2-0, both wins coming on grass at Wimbledon in straight sets, while recent match data also shows Keys has generally posted the stronger win record over the past 12 months.[1][2][11]

For comparison across platforms, Polymarket and Kalshi typically present probabilities directly, while Betfair and Smarkets are usually read through decimal odds and exchange commissions, which can make the same view look different after fees. On a market like this, a small price gap can simply reflect whether a platform is netting out commission or displaying raw implied probability, while access can also differ because some venues require fuller KYC and have narrower jurisdictional reach than others; that matters when the event is a single tennis match with a tight settlement window and little time for new information to be absorbed. The key historical frame is that this pairing has already favoured Keys twice, but not by an overwhelming statistical margin once broader form is considered.[1][2][12]

The main catalysts are straightforward: the official match order, any late scheduling changes at the National Bank Open, and whether the contest is completed within the event’s normal timing. Tennis listings on the tournament and live-score pages showed the match on 6 August 2026, and live match pages were already tracking it during the tournament window, so traders should watch for walkovers, retirements, or weather-related postponements that could push resolution towards the market’s 50-50 fallback if no winner is determined in time.[4][9][14]

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page compares National Bank Open: Marta Kostyuk vs Madison Keys specifically across Polymarket, Kalshi, Betfair Exchange and Smarkets. The live probability is the Polymarket mid; the comparison columns summarise each venue's fee structure, KYC, settlement currency and payment rails. Every CTA routes to Robinhood Prediction Markets, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

Settlement is the biggest difference between the four platforms: Polymarket on-chain in USDC (instant), Kalshi USD via CFTC (T+1), Betfair and Smarkets in local currency via bank withdrawal (T+1 to T+3). On-chain settlement clears in minutes — the fastest payout path of the four.

FAQ

Polymarket vs Kalshi — which is better?

Depends on your location. Kalshi is CFTC-regulated, US-only with full KYC. Polymarket is global, on-chain, no KYC up to $1,500. Polymarket has ~10x higher liquidity but higher regulatory risk.

What does Polymarket cost vs Kalshi?

Polymarket: 0% fees, only Polygon network costs (~$0.01/trade). Kalshi: up to 7% per trade plus spread. For high-frequency traders, Polymarket is dramatically cheaper.

Which platform has the deepest liquidity?

Polymarket — by a wide margin. Top markets reach $50-500M volume, Kalshi ~$200M cumulative, Betfair similar. Deeper liquidity means your trade moves the quote less.

Is Betfair a Polymarket alternative?

Only partially. Betfair Exchange is UK-focused with a sports-betting emphasis; they have politics markets but with thinner liquidity than Polymarket. Settlement in GBP/EUR, 2-5% commission on winnings.

Are all these platforms regulated?

No. Kalshi is CFTC-regulated (US). Betfair and Smarkets are UK Gambling Commission licensed. Polymarket operates without explicit regulation — a different risk profile than a regulated sportsbook.