Spoiler alert! This story discusses the final night of America’s Got Talent’s live quarterfinals, which aired September 8. The performance and results shows are available for next-day streaming with a Peacock subscription.The semifinals are set, as America’s Got Talent Season 21 went long on the 2026 TV schedule this week for two hours of live performances, followed immediately by an hourlong results show. What better night, then, to welcome back Heidi Klum? The former longtime AGT judge sat in for Simon Cowell, and I think it’s safe to say she enjoyed her comeback — particularly one act that left her “gobsmacked.” But I love that she also took time to shout out Cowell as he continues to recover from back surgery.Only one Golden Buzzer has been handed out per week in the AGT Season 21 live quarterfinals, and on the September 8 episode, it was Sofía Vergara who was in charge of it. Heidi Klum sounded a tad disappointed it wasn't her, and I have to admit I was, too, after last week’s guest judge Kenan Thompson got one. It worked out, though, because I think everyone was in agreement after watching Unitree’s dance with robots. Check out the performance below:Wu Yufei, a 26-year-old engineer and dancer, said he wanted to bring traditional Chinese dance to an American audience, and he used the latest technology to do it. After watching the intricately choreographed routine that had humans and robots dancing and flipping together, Heidi Klum was blown away. Actually, as she put it:I am literally gobsmacked. I have never seen anything this crazy in my life. It is absolutely mind-blowing. Howie Mandel was just as worked up over the performance Unitree accomplished, saying:This is probably one of the most amazing things I’ve ever seen in my life. They should redo a major motion picture like I, Robot, but a martial arts version of it. This is amazing! The most viral moment we’re gonna have this season.Even more viral than AGT’s young rockstar Nene Royal? I guess time will tell, but we'll definitely see them again in the finals after earning Sofía Vergara's Golden Buzzer. It's still unclear if Simon Cowell will be able to rejoin his colleagues by then. Howie Mandel reported that Cowell’s back surgery was a “success,” but no timetable has been given on his return. He was still on everyone’s minds, though, and Heidi Klum had a message for Cowell as she made her own triumphant return, saying:I’m so excited to be back, and thank you so much for my warm welcome. I miss you, Terry. I miss all my fellow judges, and I’m sad to say that I don’t see Simon. So shout out to Simon from the couch watching! Thanks for having me in your seat today. I’m really enjoying sitting in your seat today.She’s just keeping it warm for you, Simon! With all of the semifinal acts announced, the next round of competition is set to kick off at 8 p.m. ET next Tuesday, September 15, on NBC. Next week, America’s Got Talent will also return to two shows per week, with results following at the same time on Wednesday night. Tune in to see who will join Unitree and the rest of the Golden Buzzer recipients in the finals!