2 Extra Character slots
You get one character slot if you buy either Deluxe or Ultimate version. Original information about the other character slot was as follows:
Veteran Player Appreciation
For our long-standing fans and loyal players, we would like to say thank you and show our appreciation. For all players who registered the core Guild Wars 2® game prior to January 23, 2015 and who upgrade their account by prepurchasing and registering any Guild Wars 2: Heart of Thorns edition before Guild Wars 2: Heart of Thorns‘ launch, we will add one additional character slot to your Guild Wars 2 account. The process of delivering your additional character slot will take us some time, but rest assured we will get it to you as soon as possible. We’ll provide more details about the specific timing soon.
https://www.guildwars2.com/en/news/pre-purchase-community-address/