The magnitude of the announcement Saturday — and the way one singular briefing reverberated throughout the tennis ecosystem — said it all. It captured everything that the U.S. Open’s fan week, and specifically its 16-pairing mixed doubles tournament, had become.

There was the revelation that Serena Williams, the 23-time Grand Slam champion and one of the greatest doubles players of all time who recently restarted her career after retirement, would pair with Carlos Alcaraz, the 23-year-old phenom already with seven Grand Slam titles to his name.

There was the “Let’s gooooo!” with a flame emoji that Alcaraz posted to X, signaling some palpable excitement from the Spaniard returning from an injury. The U.S. Open isn’t just about the main draw anymore. As a revamped event last year, the mixed doubles tournament took off, and when fan week returned Sunday — with its staple events set to pick back up Monday — at Flushing Meadows, it remained one of the featured pieces for spectators.

But before the spotlight of mixed doubles, the early stages of fan week will unfold. Spectators can enter the Billie Jean King National Tennis Center for free to attend open practices, qualifying matches — which run from Monday through Thursday — and more by registering for a pass online, while premium tickets are available for mixed doubles and other special events. Cultural dance performances and other family-friendly activities will take place throughout the week. Marvel will have daily comic book giveaways. Fans can buy their first Honey Deuce of the season or their seventh.

And Tuesday at 7:30 p.m., five-time U.S. Open champion Roger Federer will share the court with Andre Agassi, John McEnroe and Andy Roddick — the last American men’s tennis player to win a Grand Slam tournament back in 2003 — in a ticketed exhibition at Arthur Ashe Stadium.

The six-day fan week attracted 239,307 fans last year, according to the U.S. Open — marking a 10 percent increase from 2024. The two-day mixed doubles tournament sold out. And this year, that event will begin with eight teams competing for two qualifying entries Monday before the first round and quarterfinals begin Tuesday — with fans able to watch in Louis Armstrong Stadium for free with their fan access pass beginning at 10 a.m. and in Arthur Ashe Stadium with a paid ticket beginning at 11 a.m.

Then, the ticketed semifinals begin the next day at Arthur Ashe Stadium at 7 p.m. before the final follows.

Williams and Alcaraz comprise one of the most hyped pairings, while Jessica Pegula and Taylor Fritz will be partners in an all-American one. Aryna Sabalenka and Novak Djokovic will pair. Two-time defending champions Sara Errani and Andrea Vavassori return, while Casper Ruud-Diana Shnaider, Taylor Townsend-Alexander Zverev, Emma Navarro-Tommy Paul, Belinda Bencic-Flavio Cobolli, Amanda Anisimova-Learner Tien, Alex Eala-Felix Auger-Aliassime, Leylah Fernandez-Frances Tiafoe, Elina Svitolina-Gael Monfils, Mirra Andreeva-Andrey Rublev and Jakub Mensik-Karolina Muchova are the other duos in the field.

The overhauled mixed doubles tournament has created a far different reality for the USTA before the singles matches begin Sunday. By shifting the tournament to fan week, it allowed singles stars who otherwise might not participate to join. There’s a $1 million prize. There are three sets in each match, with a 10-point tiebreak serving as the third set if needed after the first two sets are played to four points.

The interest in fan week has skyrocketed. It’s no longer just the appetizer, no longer simply a placeholder. The U.S. Open will still be defined by whoever clutches the nine-pound Tiffany & Co.-made trophy at the end. By whether an American men’s tennis player can snap the drought. By whether someone new in the women’s field, perhaps the fan favorite Pegula, can finally reach the pinnacle of the tournament.

But before then, there will be the buzz of fan week. That, by this point, has started to become a constant.”