AUSTIN, Texas — Goodbye Big 12, hello SEC. Texas and Oklahoma made their long-awaited conference switch with campus parties, carnivals, concerts and fireworks.

The move to the Southeastern Conference of two programs that were among the founding members of the Big 12 in 1996 became official on Monday, and had been three years in the making.

And to mark their move to a league where “it just means more,” Texas and Oklahoma held colorful celebrations on Sunday and Monday.

In Texas, thousands flocked to campus on Sunday in nearly 100-degree heat to take part in a carnival and concert under the famous campus clock tower.

Celebrations in Oklahoma began Sunday evening and continued with events across the state on Monday.

The SEC Network broadcast live programs from both campuses on both days.

“Since 2016, our mantra has been 'it just means more,'” said SEC Commissioner Greg Sankey, who attended both campus parties. “Oklahoma and Texas clearly live up to that mantra.”

Vic Schaefer, head coach of the Texas basketball team and former SEC coach, called the move “a divine coincidence.”

At the party in Texas, the kids played on bouncy castles, climbing walls and slides. The men cooled off their parents, who waited in long lines for autographs from Longhorns coaches and photos with Longhorns mascot Bevo and crowded into merchandise tents.

“We've been working toward this day for years,” said Chris Del Conte, Texas athletic director. “Our fans are really excited. You can see it by the turnout.”

This is a moment that college sports in general have been building toward in the era of major realignment. The exit of Texas and Oklahoma from the Big 12 has sparked countless conference moves, and more are on the way. By the first kickoff of the 2024 season, 11 so-called Power Four programs will be in new conferences.

The Big Ten will grow from 14 teams to 18 as Southern Cal, UCLA, Oregon and Washington were poached from the Pac-12. The beleaguered West Coast League also lost Arizona, Colorado, Utah and Arizona State to the Big 12 and California and Stanford to the Atlantic Coast Conference. Southern Methodist is moving from the American Athletic Conference to the Atlantic Coast Conference on Monday.

Oklahoma and Texas originally planned to join the SEC in 2025, but ultimately reached a financial settlement with the Big 12 that allowed them to leave early. And they're leaving the SEC with a lot of hardware.

Combined, the Sooners (14) and Longhorns (four) have won 18 Big 12 football titles in 25 years, with Texas taking the crown last season for the first time since 2009.

In its final year in the league, Texas won 15 regular-season or tournament league championships in all sports, as well as national titles in volleyball and rowing. Oklahoma capped its final season by winning its dominant softball program, which won its fourth consecutive national title in May. The Sooners defeated Texas in the final.

“Texas brings more tradition, more talent, more passion and more competitive spirit to the SEC,” the school said on its sports website.

All of those wins will be much harder to repeat in the SEC. Oklahoma begins its first SEC football game at home against Tennessee on Sept. 21. The Longhorns debut Sept. 28 against Mississippi State.

Since the College Football Playoffs began in 2014, SEC schools have won the championship six times.

Texas (2005) and Oklahoma (2000) were the two schools to win national football titles in the Big 12.

Some traditional rivalries are being restored, others are being torn apart.

The rivalry between Texas and Texas A&M is revived. It was on hiatus since A&M left the Big 12 and joined the SEC in 2012. Oklahoma's rivalry between Oklahoma State and Bedlam has broken down.

Texas spiced things up with Texas A&M last week when it lured Aggies head coach Jim Schlossnagle to Austin. At his introductory press conference, Schlossnagle warned Longhorns fans that the SEC is the “major league” of college baseball. The league has won the last five national championships.

The celebrations in Oklahoma began Sunday evening with a 5K run through the middle of campus and a fireworks display.

On Monday morning, former Sooners head coach Barry Switzer co-hosted a celebratory breakfast in Tulsa. Later in the day, Oklahoma planned a campus party at the football stadium with live music and entertainment.

“We are thrilled to join the SEC. Our teams are set up for success and look forward to competing against many of America's most outstanding universities,” said Oklahoma athletic director Joe Castiglione.