As the World Cup approaches, the sports-focused prediction market Kalshi has grown its open interest to approximately $650 million. Kalshi holds slightly over 50% of the market share in prediction market open interest. Polymarket follows closely with over $500 million in open interest. Kalshi and Polymarket are far ahead of other challengers. Predict Fun is the only market with open interest in the tens of millions, while other markets only have open interest in the millions or tens of millions.