They have not stated, however if you look at the gameplay reveal, it looks like PHB Point Buy.
Custom character creation
https://www.youtube.com/watch?v=XJhawYZwvPI&feature=youtu.be&t=1836 (+1 Cha for Lightfoot subrace added, equals standard array. They did not have the main race's bonus listed at the time.)
Astarion's character sheet
https://www.youtube.com/watch?v=XJhawYZwvPI&feature=youtu.be&t=3030 (racial bonuses not applied yet, equals standard array.)
