Alexander-Arnold, 21, was handed his first-team debut by Klopp in October 2016 and has become a pivotal player for both club and country since.
And Klopp has been delighted by the defender’s progress.
“I have known Trent Alexander-Arnold since he was 17 years old,” Klopp told the BBC.
“He was a big talent but we were not sure he could do it physically. Now he is a machine – so he is a big surprise.”
Klopp added that he believes his Liverpool team are motivated enough to achieve even more.
“The conscious decision we made with the boys was, as Liverpool players, it was not about winning one thing. It is about winning and there is no limit.
“The moment we did it was important – but it did not give us a feeling it was done.
“We like to think we would meet up in 20 to 30 years, look back and mix up the years. Was it 2019 or 2020?
“So far, so good. We try to squeeze everything we can get from our time together. There is no pressure, it is just opportunity.”