The Sims 4 players with Windows systems will finally be able to play a fully 64-bit compatible version of The Sims 4 in December. This change will allow The Sims 4 to utilize more than a 4GB of RAM, which will hopefully make the game more responsive and stable when playing heavily populated lots.
Origin will automagically decide which version of The Sims 4 to load once this patch is released – presumably some time in December before the release of the Get Together expansion pack.