According to Ten Hag and Borussia Dortmund, even if they didn’t use the same words.

My definition: world-class is a player that’s either the best in his position in the world or very close to the best player in this position.
For example, you could argue that Harry Kane is the best striker in the world right now (and that’s coming from an Arsenal fan!), but Haaland obviously deserves the same label.
With that in mind, I would say Saka, Rice, and Saliba are there. Odegaard and Martinelli are very close, I think Ben White was in that second group last season too.