[Kalshi and Polymarket Open Interest Drops by 20% as World Cup Fever Subsides] According to The Block, on the eve of the World Cup final, the combined open interest of Kalshi and Polymarket dropped by 20% from its peak of approximately $2 billion in early July, falling from nearly $1.8 billion to around $1.5 billion. Kalshi's sports event trading volume declined from a peak of approximately $9 billion during the week of July 5 to about $4 billion, while Polymarket's volume dropped from around $2.3 billion to $740 million. During the World Cup, sports events accounted for about 80% of the total trading volume on both platforms. Spain defeated Argentina 1-0 on Sunday to claim their second World Cup title in team history. Polymarket profit and loss data compiled by DeFiOasis shows that 194,000 addresses traded on Polymarket's World Cup champion market, with roughly two-thirds incurring losses.