Polymarket US Combos hit 20% share in first week as multi-leg contracts surge
Polymarket US Combos, multi-leg event contracts, surpassed 20% of exchange volume within a week of exiting beta, matching the adoption curve Kalshi saw with similar products. Kalshi's non-sports event contracts now routinely draw nine-figure daily trading volume. Robinhood and Underdog are also active in the space, alongside the two leading platforms. The data points suggest retail traders are gravitating toward bundled or enhanced contract structures.
Multi-leg contracts are becoming the dominant trading format at both leading CFTC-regulated platforms. Polymarket's Combos reached one-fifth of total volume within days, while Kalshi's comparable offering had already become its largest category. That shift forces Robinhood and Underdog to accelerate their own product roadmaps or risk losing active traders to venues with more sophisticated contract structures.
For market makers, the move from simple yes-no binaries to complex legs demands new pricing models and wider spreads until flow patterns stabilize. The timeline is immediate: Novig's recent entry with a sweepstakes-converted user base adds pressure for incumbents to differentiate on product rather than brand. Platforms that lag on multi-leg or sports combos will see their most valuable traders migrate to venues offering deeper strategy expression. The competitive race is now for contract innovation, not just market share.