Polymarket US began processing multi-leg sports contracts on Aug. 5 through an API-only beta that never surfaced in its consumer app. The launch lands as rival Kalshi is reported to be extending maker fees to its own parlay product, a change its published fee schedule does not list.
Key Takeaways
Polymarket US cleared $7.4M in parlay volume in an API-only beta that opened Aug. 5.InGame counted $25M in Kalshi parlay taker fees over the first 16 days of August.Kalshi’s fee schedule shows no upcoming changes at the time of writing.The option does not appear in the Polymarket US app, the exchange has not widely launched a desktop site, and the combos documentation sits under the institutional section, available only to explicitly enabled API users.
The underlying product is the Combinatoric Athletic Outcome Contract: every leg must settle on the chosen side for the contract to pay $1.00; if any single leg misses, it pays nothing. The schema accepts two to 10 legs. Polymarket US self-certified it on May 20 and amended the terms on July 14, with the revised products listable no earlier than July 28. The first trade came eight days after that. Polymarket’s offshore site, which blocks U.S. traffic, had been running parlays since June 10.
What the schedule does show is how the economics fall on parlay traders. The 1.75% peak is a share of contract value, not of money staked, and it applies at 50 cents. Parlays price at long odds by construction. At one cent, 100 contracts cost $1.00 and carry a seven-cent fee, or 7% of the stake. At five cents the rate is 6.8%, at 10 cents 6.3%, and only at a coin flip does it fall to 3.5%. The cheapest fees on the curve sit where parlay traders never are.
