The Dutchman claimed his third consecutive world championship in record-breaking fashion in 2023, winning 19 of the 22 races and scoring more than double the amount of points achieved by teammate Sergio Perez.
Verstappen set several new records, including most wins and most consecutive wins, in what was the most dominant season by a driver in F1 history.
“He’s just grown and grown as a driver and as a human being,” Horner told Motorsport Magazine.
“I think the speed and skill has always been there. He’s just rounded it with experience now. And the capacity that he has within the car to be taking on and thinking about other things is outstanding.
“To be able to read the race, to be able to nurse tyres the way he does, to understand what he needs to deliver strategically to make something work, is extraordinary and I think he’s just very much the complete driver.
“We knew he was a very special talent, but only time would tell what that talent would yield, and it needed us to give him the tools to deliver as well. And thankfully, we’ve been able to do that, and he’s used them in the best possible way. And so what he’s done the last three years, it’s just been sensational.
“I think Max, where he is at the moment is the best driver currently in Formula 1. He’s the world champion, and he is - without a shadow of a doubt - the very best driver Formula 1 currently has.”
Horner also acknowledged that Perez has “the hardest job in the pit lane” being Verstappen’s teammate.
“To have won 21 out of 22 grands prix is insane,” he said of Red Bull’s achievements in 2023. “And something that the whole team can feel rightly proud of, that they’ve built and delivered and executed this weapon of a car.
“Max has been out of this world. Checo’s done a great job as well, the first time we’ve ever been first a second in a championship. It’s been an unbelievable year for us.”