Blizzard has stated that players will gain about 40% more experience while leveling in Diablo 4’s upcoming Season 2!
Diablo 4 Season 2 Liveblog
As Joe Shely has explained in the Diablo 4 Season 2 Developer Update, all experience changes coming with Season 2 – most importantly, World Tier experience bonus becoming multiplicative – will, cumulatively, increase player experience gained by up to 40%.