The experience to get from level 89 to 90, 684,225, it more than the experience to get from level 1 to 50, which is 681,310.
By the time you've reached level 90, you've accumulated at least 9,957,710 experience.
From level 80 to 90, you gain over 4,800,000 experience. That's more than the amount to get from level 1 to 79, but not from 1 to 80. So almost half your experience comes from being an Archmage.
At the current rate experience rates are going, by level 160, we can expect to have 1,274,586,880 (or more) experience. That means we will break the 32-bit integer by level 167. That means the total experience will start going negative.
Getting from 99 to 100 will take over 1,000,000 experience. Yep. That's right.