Like in The Witcher2 the information is there and INGAME.
You will not have to consult guides or external wikis.
During the GOG livestream combat /Q&A they confirmed it again.
If you have a savegame from a previous game you can import a "world state", if not there will be a discussion with an NPC ingame that will help you decide how previous events turned out and give you enough information to understand the world and motivations/backgrounds of characters.
There is also a journal/beastiary giving you more info about the lore and history of the world of the witcher.