Polymarket's regulated US exchange has started processing multi-leg combo trades in a beta test, months after the offshore version of the product debuted through a request-for-quote (RFQ) pricing system during the FIFA World Cup.
Both versions of the product price trades through a request-for-quote mechanism rather than Polymarket's standard central limit order book.
A trader submits a request to combine several outcomes into a single position, and market makers have 400 milliseconds to return a price.
The trader then has five seconds to accept the best offer. Market makers can enable a "Last Look" feature, which adds a further one-second window for them to accept or reject the fill after a trader agrees to a quote.
Each leg of a combo must settle in the trader's favor for the position to pay out; one incorrect leg voids the entire ticket. Because pricing runs off the visible order book, users typically can only take the "yes" side of a combo unless they access the market through the API — a dynamic that tends to leave casual bettors, who sit overwhelmingly on "yes," on the losing side of the trade.
From offshore debut to regulated beta
The offshore platform, which blocks US IP addresses, opened combo trading on June 10, covering moneyline, spread and total markets.
Polymarket confirmed the sports-only release on X, stating, "combos are now live." No timeline has been set for extending the product to political contests, breaking-news markets or other event categories on either platform.
The regulated US exchange self-certified its version of the product with the Commodity Futures Trading Commission (CFTC) in May under the name "Combinatorial Athletic Outcome Contracts" (CAOCs), then took roughly 10 weeks to process its first trade, on August 5.
The product remains in beta: the option to build a combo is not yet visible on the Polymarket US app, the exchange has not broadly launched a desktop site, and all activity to date has occurred through this test environment. Beta users are limited to combos of up to 10 legs.
In the days following the August 5 debut, combo trading on Polymarket US reached $7.4M in volume, with $928,093 in taker-side stakes across 16,173 trades — the bulk of it recorded since last Thursday.
That test-phase weekend volume exceeded the parlay volume Kalshi generated in its first several days after opening the product to its full user base.
Polymarket has also opened a public API endpoint for combo market data that does not require the authentication tied to its central limit order book, allowing outside trading dashboards and analytics services to pull combo pricing independently.
Fees, settlement and liquidity still unsettled
Polymarket has not finalized how fees will apply across the multiple legs of a single combo, or how settlement will work when one leg resolves before the others.
With fewer market makers pricing combos than single-outcome markets, the company has acknowledged the product could see thinner liquidity and wider bid-offer spreads than its standalone contracts.
Kalshi's parlay business keeps growing
While Polymarket US worked toward its beta launch, Kalshi's parlay volume rose from $4.77B in May to $13.78B in July, and August volume is tracking toward a similar figure despite a lighter sports calendar.
Kalshi generated $25M in parlay taker fees in the first 16 days of August alone. Its parlay product currently permits combos of more than 30 legs, well beyond the 10-leg cap in Polymarket's beta.
Kalshi is preparing to introduce maker fees on parlays, a category where market makers previously traded without charge and at times qualified for liquidity incentives.
The new fees would follow the same schedule applied to Kalshi's other contracts, under which maker fees run at roughly a quarter of taker fees and vary by odds — higher near even money, lower toward the extremes. As a share of volume, parlay fees remain lower than those on most other contract types, though the category's overall volume still makes it a significant contributor to Kalshi's fee revenue.
The two platforms' competing pushes into multi-leg sports wagers coincide with a separate dispute over product origination. Polymarket has been reviewing whether Kalshi mirrored its business model, compiling a roughly 12-item internal document referred to as "Copycat" that catalogs instances in which Polymarket believes Kalshi released similar products shortly after its own — spanning contracts tied to sports, weather and the conflict involving Iran.
Polymarket's head of marketing, Matthew Modabber, confirmed the internal review in a phone interview with The Post: "There have been a couple too many coincidences."
Polymarket's Shayne Coplan went further, accusing the rival platform of deliberate imitation: "There is bad intention in how they copy us. They're breathing down our neck."
Dingnews.com 19/08/2026