Trade: Saint-Malo: Sofia Costoulas vs Ayla Aksu

Market context

Sofia Costoulas and Ayla Aksu are scheduled to compete in a professional tennis match at Saint-Malo on 28 April 2026. The market currently reflects 100% implied probability for Costoulas advancing, with the settlement window closing on 5 May 2026 at 09:00 UTC. The match will resolve to either player based on match outcome, or to 50-50 in the event of cancellation, tie, or delay exceeding seven days without completion.

The 100% probability on Polymarket's order book suggests either substantial backing of Costoulas or minimal liquidity at current odds. Historical precedent in lower-tier professional tennis shows that pre-match probabilities of this magnitude typically reflect significant disparities in ranking, recent form, or head-to-head records. Without recent published rankings or match history between these players readily available, the extreme probability warrants scrutiny—such pricing often corrects when additional information surfaces or when traders with opposing views add liquidity to the book.

Key catalysts include confirmation of both players' participation as the match date approaches, any injury announcements in the week prior, and weather conditions at Saint-Malo on the scheduled date. The early morning start time (05:00 ET) may affect player availability or performance. Traders should monitor the WTA Challenger circuit schedule and any official Saint-Malo tournament updates for withdrawals or rescheduling notices, particularly given the seven-day delay threshold that would trigger a 50-50 resolution.

Resolution source

This market settles from the official outcome published at https://www.wtatennis.com/scores. A proposer submits the final result to the UMA optimistic oracle on Polygon; the two-hour dispute window closes and payouts clear in USDC.

How to trade this market step by step

The mechanics for trading "Saint-Malo: Sofia Costoulas vs Ayla Aksu" are the same as any other PolyGram event contract. Each YES share resolves to $1 if the event happens, or $0 if it doesn't. The current price between 0¢ and 100¢ is the market's probability estimate, set live by the order book.

1. Sign in on polygram.ink with your email — no full KYC under $1,500 lifetime trading volume.
2. Deposit USDC on Polygon (lowest fees, ~$0.01 per transaction) or Ethereum. Funds credit after 12 confirmations.
3. Pick a side. Buy YES if you believe the event will happen; buy NO if you think it won't. The current YES price reflects the market's collective probability.
4. Size your position. If you stake 100 USDC at 50% YES, you'll receive shares that pay $200 if YES resolves true — a 100% gross return. If NO resolves, your shares are worth $0.
5. Set risk controls (optional). Stop-loss, take-profit, and limit-order types all supported. Use the trade ticket's slippage box to cap your maximum entry price.
6. Wait for resolution. When the event resolves on-chain via the UMA optimistic oracle, the winning side settles to 100¢ automatically and USDC hits your balance within seconds. Withdrawable to any wallet you control.

How active is this market?

$27K in lifetime turnover and $0 of resting liquidity puts this market in the around the median by volume for tennis contracts on PolyGram. Order-book depth is thin — large orders may need to be split across the book or executed as limit orders.

The market has been open for under a month — fresh enough that information asymmetry remains a real factor.

Higher-volume markets tend to have tighter spreads and faster price discovery — meaning the displayed YES/NO percentages are more likely to reflect the true crowd-implied probability rather than a single trader's directional view.

Key terms

YES / NO share

A binary outcome token that pays $1.00 if the underlying claim resolves true (YES) or false (NO), and $0 otherwise. The market price between 0¢ and 100¢ is the implied probability.

CLOB

Central limit order book. The matching engine that pairs YES buyers with NO buyers (effectively the same trade). Polymarket's CLOB on Polygon executes trades on-chain via the conditional-tokens framework.

Liquidity

USDC capital sitting in resting limit orders inside the order book. Deeper liquidity means smaller slippage on large trades and a tighter bid-ask spread.

UMA optimistic oracle

The on-chain dispute system that settles each Polymarket market. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution.

Slippage

The difference between the displayed mid-price and your fill price. Affects market orders most; limit orders avoid slippage but may take time to fill.

Conditional token

ERC-1155 outcome share issued by Gnosis Conditional Tokens on Polygon. The token type that resolves to $1.00 or $0.00 at settlement.

See the full prediction-market glossary →

Frequently asked questions

Risk and regulatory note

Prediction-market positions can lose 100% of staked capital. Outcomes are uncertain by definition — historical accuracy of crowd-implied probabilities is high in aggregate but not for any single market. PolyGram does not provide investment advice. Trade only with capital you can afford to lose.

Regulatory status varies by jurisdiction. Germany, the United States, and most EU countries treat Polymarket-style event contracts under one of three frameworks: financial derivative, gambling product, or unregulated novel asset. Consult local counsel before trading.

Related prediction markets

Explore more prediction market odds and trading opportunities on PolyGram:

• All tennis prediction markets
• How prediction markets work
• Browse all prediction markets on PolyGram
• Top prediction market traders
• Back to PolyGram home