Sarah Holding, a producer on The Sims 4, has confirmed on Twitter today that the largest lot size in the game is 50×50 as of right now. The game does not currently have a 64×64 lot.
While some may like to utilise the full 64×64 lot, I don’t think I’ve ever actually filled a lot that size 😛
@EJamonica The biggest lots are 50×50. The Sims 4 does not have 64×64 lot at this time.
— Sarah Holding (@SimGuruSarah) July 1, 2014