Each driver gets the chance to choose a race number on their F1 debut. For example, Oscar Piastri chose race number 81 for next season and Nyck de Vries will also soon announce which number he will drive with next year. In principle, after that, that race number is fixed for the rest of the driver's career. That number may only be changed if the driver becomes world champion: then he may choose to drive with number 1 for the coming season.
'How often do you get that chance?'
Verstappen chose to swap his number 33 for number 1 this season, so next season he will do so again. "I think it's the very best number there is for a driver," Verstappen explained. "How often do you get the chance to drive with start number 1 in your Formula 1 career? You never know. I can always go back to number 33 if I am no longer world champion. But as long as I am world champion, I will use number 1 every year."
The new system with race numbers was introduced in 2014. That year, Sebastian Vettel drove with number 1, making it the last time anyone drove with that number until this season. Lewis Hamilton always continued to use his number 44 and Nico Rosberg retired immediately after winning his title.