The Germans announced the news on Twitter:
"I tried to sign Ethan on loan at Derby last year so I'm a big fan, but with the minutes he played last year, in the interest of Ethan and of Chelsea, the idea he can play a lot of games somewhere could be good for him.
"I really wanted to work with Ethan this year. That's a slight disappointment, but it's to benefit him. In midfield and defence we have a lot of quality, so each player is a case by case."
The Welsh teenager made his senior Chelsea debut in 2017 and has been highly regarded as a talent for the future since. While he's a natural fit as a defensive midfielder, he can also play as a centre-back, where he has seen most playing time for the Blues so far.
That versatility should come in handy in Germany, per Goal's Ronan Murphy:
Football.london's Oliver Harbord thinks it's a smart move:
Leipzig manager Julian Nagelsmann gave plenty of minutes to his youngsters during his spell with Hoffenheim, and he's expected to do the same at his new club. The Red Bulls have a young squad, likely one of the reasons they hired the 31-year-old tactician.
But while he should be a good fit under Nagelsmann, there are plenty of risks involved with this loan move for Ampadu.
Leipzig are a UEFA Champions League-caliber team with plenty of talent up and down the squad. In defence, Ampadu will compete with two of the best prospects in all of Germany, Dayot Upamecano and Ibrahima Konate. The midfield competition will also be fierce, as RB employ Amadou Haidara, Tyler Adams, Christopher Nkunku, Diego Demme and Kevin Kampl.
Consistent minutes are far from guaranteed in Leipzig, and Ampadu will have to earn his spot in the squad. If an increase in playing time was Chelsea's main reason for the loan, they could have picked a smaller club where starts for the talent were far more likely.