LeBron James made his Polymarket partnership public in a video posted to X, showing the NBA star entering what he called Polymarket HQ before reaching a sports-themed floor. Polymarket has promised a full reveal on Tuesday, while earlier reporting said the campaign would focus on football markets and launch in the coming week. James's exact role and the deal's financial terms have not been disclosed. The arrangement follows the expiration earlier this summer of James's DraftKings endorsement deal, underscoring intensifying competition between sportsbooks and prediction-market platforms. Polymarket users trade outcome contracts on events including sports, politics and economic data. NBA rules permit player endorsements of prediction markets but prohibit players from promoting contracts tied to NBA games; the NFL and PGA Tour reportedly prohibit such agreements. Prediction-market activity has grown rapidly, with sector volume exceeding $20 billion a month by January, compared with roughly $1.2 billion in early 2025. Earlier Dune Analytics data put combined notional trading volume across nine platforms at $49.9 billion in June, $56.4 billion in July and $50.7 billion in August. Reports differ on trading linked to James's next team, citing more than $245 million and more than $273 million, respectively. Polymarket's expansion comes amid legal challenges from U.S. cities and states, even as the company sought $400 million at a $15 billion valuation in April and received a $2 billion commitment from Intercontinental Exchange.