The final round of the U.S. Chess Championship delivered unexpected drama. Wesley So entered with a full-point lead but fell to a loss against Sam Sevian in a heavy-piece endgame. At the same time, Fabiano Caruana won decisively against Awonder Liang, forcing a playoff between the two competitors on Thursday. Caruana had expressed near-total pessimism before the round, saying there was essentially no chance So would lose. The American number-one and defending champion managed to convert a winning position despite those low expectations.

Caruana's victory came through a carefully executed kingside attack in the Tarrasch Defense. His second, Grigoriy Oparin, had shared the interesting 6.Bf4 idea at Wijk aan Zee earlier in the year. The critical breakthrough came with 26.Ne4!, launching a second wave of attacking pressure after the first assault stalled. Sevian, despite sitting in last place before the round, brought extensive experience against So, boasting three career victories and zero losses in their head-to-head matchup.

The path to the title looked clear for So, who had built a 48-game unbeaten streak in the U.S. Championships. A draw would have secured the championship even with Caruana's win, but Sevian proved too formidable. Sevian explained his success by saying he understands So's classical chess far better than his opponent's approach to faster time controls, where So excels at setting tactical traps. The playoff between Caruana and So features rapid games first, followed by additional rapid rounds if necessary, then blitz matches, and potentially armageddon.

Rachael Li clinched the U.S. Women's Championship after drawing with Anna Zatonskih in the final round. The 16-year-old became the youngest first-time winner of the event, earning $45,000 in combined prize money. Li also secured her first IM norm with two rounds remaining and gained 50 rating points. Alice Lee finished second and both players qualify for the next FIDE Women's World Cup.

Zatonskih declined a three-move repetition despite having no mathematical chance to win the tournament, choosing to let the game continue because she felt a draw would be unfair to Lee's playoff hopes. Li reached an opposite-color bishop endgame that offered no winning chances for either side. The teenager credited her brother, GM Ruifeng Li, with extensive preparation and mental support. She acknowledged that nerves finally caught up with her the night before the final game, despite maintaining composure throughout the tournament.

The women's championship saw notable performances from other competitors. GM Irina Krush finished in sole third place and gained 11 rating points despite hanging her queen early against Li. IM Rose Atwell recorded a victory featuring a queen sacrifice. Lee finished with a win against IM Anna Sargsyan and said she played poorly overall, though her results exceeded expectations.