Polymarket US open interest nearly doubles to $111M after World Cup winds down

Polymarket’s US-regulated prediction market has hit $111.4 million in open interest, nearly doubling since the 2026 FIFA World Cup wrapped up in mid-July. The platform now accounts for 54% of total Polymarket volume, a striking milestone for a product that didn’t exist until December 2025. The growth is especially notable because it runs counter to the broader trend. After the World Cup concluded on July 19, combined open interest across prediction markets, including competitor Kalshi, dropped by roughly 20%. Polymarket US, meanwhile, went the other direction entirely. The World Cup hangover hit everyone else harder The 2026 World Cup was, by any measure, a bonanza for prediction markets. Polymarket’s soccer category alone generated over $2 billion in volume during the tournament’s first ten days. Kalshi’s peak combined open interest during the event hovered around $2 billion. Kalshi’s open interest slid from its peak near $2 billion down to approximately $1.5 billion by late July. Polymarket US bucked this pattern. Its open interest continued climbing through August, reaching $111.4 million by August 22. What’s different about Polymarket US The original Polymarket operates as a cr...