Polymarket Opens Parlays to Everyone as Kalshi Starts Charging Makers

The two largest US prediction market venues moved on the same product on the same day, in opposite directions. Parlays are the sportsbook's highest-margin invention, and both of them reached the market by self-certification.

• Polymarket US opened parlay trading to the public on 21 August, having self-certified the product in May, begun testing on its CFTC-regulated exchange on 5 August and ramped volume from 12 August
• Parlay volume on the Polymarket US exchange reached $8.7 million by 7pm Eastern on Thursday, of which takers staked $1.2 million; the earlier test environment recorded roughly $7.4 million across 16,173 trades
• Kalshi introduced maker fees on its own parlays the same day, having previously charged market makers nothing on the product
• The new Kalshi maker fee is set at half its taker rate, which is higher than most maker fees on the venue, and uncorrelated NFL parlays remain exempt
• Both venues list parlays under self-certification, the mechanism CME's Terry Duffy attacked at the CFTC's own advisory committee the day before

Two Venues, One Product, Opposite Moves

Polymarket US made parlays generally available on 21 August. The path there was deliberate and slow: the company self-certified the contracts with the Commodity Futures Trading Commission in May, processed its first trade on the regulated US exchange on 5 August, and let volume build from 12 August before opening the product to all users.

The numbers it has published are worth reading carefully. Parlay volume on Thursday reached $8.7 million by 7pm Eastern, but takers, the side that pays a fee and initiates a position, staked $1.2 million of that. The test phase recorded around $7.4 million across 16,173 trades. On both measures the great majority of activity is on the maker side, which is what a market looks like when professional liquidity providers are quoting into thin retail demand. For scale, the sector as a whole turned over $50.6 billion in July, with Kalshi taking 74.5% of it.

Kalshi moved in the other direction on the same day. It began charging maker fees on parlays for the first time. Until now, makers on Kalshi paid nothing, while takers did, and because parlay takers lose more than they win over time, quoting parlay prices without a fee was a durable edge for anyone able to price correlation. The new maker fee is pitched at half the taker rate, which is above most other maker fees on the exchange. Uncorrelated NFL parlays are carved out and remain free to quote.

Neither venue needed permission in the ordinary sense. Both products arrived through self-certification, under which a designated contract market lists a contract by filing and certifying that it complies with the Commodity Exchange Act. It is the same mechanism CME Group chairman Terry Duffy attacked at the CFTC's inaugural Innovation Advisory Committee meeting on 20 August, when he noted that 2,500 self-certifications had been filed since January 2025 and none opposed.

The Product They Both Just Prioritised Is the Sportsbook's Best Earner

A parlay is several correlated or uncorrelated outcomes bundled into one position that pays only if every leg lands. In regulated sports betting it is the single most profitable product on the shelf, carrying a hold percentage several times that of a straight bet, and it is where operators direct their promotional spend for exactly that reason. Its arrival at scale on two CFTC-regulated exchanges is therefore the clearest signal yet about what these venues are becoming. An exchange that lists wheat futures does not need a combination product; the demand for one comes from customers who want a small stake at long odds, which is a betting preference rather than a hedging need. That does not settle the legal question, and courts have split on it, most recently in Washington. It does make the commercial answer harder to argue with.

Kalshi's Carve-Out Says Exactly Where It Wants Liquidity

The interesting detail is not the fee, it is the exemption. Kalshi will charge makers on parlays generally, but not on uncorrelated NFL parlays. Correlation is the whole risk in pricing a parlay: legs that move together are far harder to quote and far easier to pick off with information. By taxing the correlated book and leaving the uncorrelated NFL book free, Kalshi is paying market makers to supply depth precisely where pricing is safest and the football season is about to generate the most volume, while taking revenue from the part of the book where its own edge is largest. That is sophisticated exchange design. It is also, unmistakably, the behaviour of a business optimising a betting product, from a venue that has previously withdrawn a product under public pressure rather than on a regulator's instruction.

Self-Certification Was Questioned on Thursday and Used on Friday

The timing is the story for regulators. On 20 August the chairman of the largest US derivatives exchange told a CFTC advisory committee that 2,500 self-certifications had gone unopposed and that individual-outcome sports contracts are open to manipulation. Chairman Michael Selig called the characterisation fake news. On 21 August, a self-certified parlay product opened to the public, and a competitor restructured the fees on its own. Nothing improper happened in that sequence: self-certification is the law as written, and both venues followed it. But it demonstrates the gap Duffy was pointing at. The mechanism is fast enough that a product can go from filing in May to general availability in August without the regulator ever having to form a public view, and it is fast enough that the argument about whether it should exist happens after the volume does.

Both exchanges now offer the sportsbook's most lucrative product, priced like exchange market making and cleared like a derivative. The states arguing that this is gambling did not need a better exhibit, and they have been handed one anyway.