TLDR
- Polymarket US began testing multi-leg sports contracts on Aug. 5 through an API-only beta that never appeared in its consumer app.
- The beta logged 16,173 trades worth $7.4 million in volume and $928,093 in stakes.
- Kalshi collected about $25 million in parlay taker fees during the first 16 days of August.
- Reports that Kalshi will add maker fees to parlays on Aug. 20 trace back to a trader’s post on X, not to Kalshi.
- Kalshi’s published fee schedule currently lists no upcoming changes to its parlay pricing.
Polymarket US started processing multi-leg sports contracts, known as parlays, on Aug. 5. The launch came through an API-only beta. It has not appeared in the exchange’s consumer app.
The beta arrived 11 weeks after Polymarket US certified the product with federal regulators. Data from InGame shows 16,173 trades during the test. Total volume reached $7.4 million.
Stakes from the taking side of those trades came to $928,093. Most of the activity happened after Aug. 13. Volume figures count both sides of a trade, so the stake number reflects money actually put up.
The parlay option does not show up in Polymarket’s app. The exchange also has not launched a full desktop site. Documentation for the product sits in a section only visible to approved API users.
A Slow Rollout After Certification
The underlying contract is called the Combinatoric Athletic Outcome Contract. Each leg in the bet must win for the contract to pay out $1.00. If one leg loses, the whole contract pays nothing.
The contract can include between two and 10 legs. Polymarket US filed the product with regulators on May 20. It amended the terms on July 14.
The revised version could not be listed before July 28. The first trade came eight days later, on Aug. 5. Polymarket’s offshore platform, which blocks U.S. users, has offered parlays since June 10.
Kalshi has had the U.S. parlay market mostly to itself while Polymarket built out its version. Kalshi’s parlay volume rose from $4.77 billion in May to $13.78 billion in July. That stretch overlapped with heavy prediction market trading tied to the World Cup.
InGame reports Kalshi collected about $25 million in parlay taker fees over the first 16 days of August. That total came during a slow stretch for sports. Kalshi’s combo bets are limited to professional football, professional basketball, and its mention markets.
How the Fee Structures Compare
Reports spread this week that Kalshi plans to add maker fees to its parlay product starting Aug. 20. The claim traces back to a trader’s post on the social platform X on Aug. 15. Kalshi itself has not confirmed the change.
Kalshi’s published fee schedule does not list any parlay or combo fee changes. Its section for upcoming updates states none is scheduled. The exchange does note that some products carry their own separate fee schedule.
Kalshi’s standard fee tops out at 1.75% of contract value at the 50-cent price point. Parlays tend to price at long odds, far from that midpoint. At one cent, the fee works out to about 7% of the money staked.
At five cents, the fee runs about 6.8%. At 10 cents, it drops to 6.3%. The lowest point on the fee curve sits near a coin-flip price, a spot where parlay bets rarely land.
Polymarket US moved in the other direction. Its fee schedule, in place since July 1, tops out at $1.50 per 100 contracts, below Kalshi’s $1.75 cap. Market makers on Polymarket also receive a rebate tied to a formula based on contract price.
That rebate can reach $0.31 per 100 contracts. Traders who clear $250,000 in monthly volume qualify for weekly rebates. A separate rule lets the exchange grant tier status to traders who prove trading volume on a competing platform.
The two platforms also price parlays differently. Kalshi runs its combo bets through a private quote process, where a trader only sees the best offer. Polymarket’s process is optional, letting combo trades also fill on its open order book.
Sportsbook operators have already stepped into market-making roles on both exchanges. Rebate structures often decide where those firms choose to post trading size. That dynamic could shape how much liquidity each platform builds for parlay bets going forward.
