Polymarket US has begun testing multi-leg sports contracts, entering a market where rival Kalshi has generated millions of dollars in fees and is reportedly considering charging makers on its own parlay products.
The first Polymarket US multi-leg sports trade was processed on 5 August, 11 weeks after the exchange certified the product with federal regulators, according to an analysis of its trading data by InGame.
The analysis identified 16,173 trades with total volume of $7.4m and $928,093 in stakes from the taking side. Most of that activity came after 13 August. Prediction-market volume includes both sides of each transaction, meaning the stake figure is a more direct indication of the money actually committed by traders.
Polymarket US is running the product through an API-only beta. It is not visible in the consumer app, while the exchange has yet to launch a widely available desktop site. Documentation for the contracts is located within Polymarket’s institutional section and is accessible only to users whose APIs have been specifically enabled.
The product is called the Combinatoric Athletic Outcome Contract. For a contract to pay out $1, every selected leg must settle on the chosen outcome. If even one leg fails, the contract pays nothing. The product can contain between two and 10 legs.
Polymarket US self-certified the contract on 20 May and amended its terms on 14 July. The revised products could not be listed before 28 July, with the first trade taking place eight days later. Polymarket’s offshore platform, which blocks users in the United States, has offered parlays since 10 June.
Kalshi has had the multi-leg sports market largely to itself during that period. Its parlay volume increased from $4.77bn in May to $13.78bn in July, during a period of record prediction-market activity surrounding the World Cup. Those figures, like other prediction-market volume figures, count both sides of every trade.
InGame calculated that Kalshi collected $25m in parlay taker fees during the first 16 days of August, despite a relatively limited sporting schedule. Kalshi’s combos are described as covering professional football, professional basketball and its “mention” markets. That means the category is narrower by sport than the possible number of legs might suggest.
Reports that Kalshi intends to introduce maker fees for parlays from 20 August originated with a trader’s post on X circulated on 15 August, rather than an announcement from the exchange.
Kalshi’s published fee schedule does not list a combo or parlay series among the products shown, while its section on upcoming changes says no such change is scheduled. However, the schedule also states that products which “have their own fee schedule” may be excluded from the main table, leaving open the possibility that a separate arrangement could apply.
The listed fee structure illustrates the cost faced by parlay traders. Kalshi’s peak rate of 1.75% is calculated against contract value rather than the amount staked, and applies when a contract is priced at 50 cents.
Because parlays are typically priced at long odds, the effective charge can be considerably higher. One hundred contracts priced at one cent cost $1 and carry a seven-cent fee, equivalent to 7% of the stake. At five cents, the effective rate is 6.8%; at 10 cents it is 6.3%. Only at 50 cents does it fall to 3.5%. The lowest fees therefore apply at prices that parlay traders are unlikely to use.
Polymarket US has adopted a different approach. Its exchange-wide fee schedule, in force since 1 July, sets a maximum charge of $1.50 per 100 contracts, compared with Kalshi’s $1.75. It also offers makers a rebate calculated as 0.0125 × C × P × (1−P), credited when the trade is filled and worth up to $0.31 per 100 contracts.
Takers who generated $250,000 in notional volume during the previous calendar month can qualify for weekly rebates. Under Polymarket’s Accelerated Tier Placement scheme, traders can also receive a tier based on verifiable trailing 30-day notional volume at a competing venue.
No separate exception for combos appears in Polymarket US’s published schedule. As a result, a market maker quoting parlay contracts could receive payment from Polymarket US and, unless the reported Kalshi change is introduced, face no maker charge on Kalshi. Sportsbook operators have already acted as market makers on both venues, making fee rebates an important factor in deciding where they place liquidity.
The exchanges also differ in how their products are traded. Kalshi’s combos are described as using a request-for-quote, or RFQ, process, in which market makers privately quote the opposite side and the trader sees only the best available offer.
Polymarket’s documentation presents RFQ as optional. Its combo contracts can trade through the ordinary order interface on a dedicated order book, while RFQ orders enter that same book and may match with resting liquidity. Traders can buy or sell individual legs.
Polymarket US’s launch follows a pattern in which product roadmaps have previously been inferred from API material on both platforms. Such technical details have offered early indications of features that may later reach the exchanges.
Kalshi has also removed all sports-mention markets, which involved contracts on whether a broadcaster would say a particular word. The removal was linked to the Commodity Futures Trading…
