Note sure if it has changed, but this is the last info I could find:
The new series will premiere on May 21, 2017, and consists of 18 episodes.
found this :
The limited series is set in present day, picking up 25 years after the events of the season two finale. All episodes were written by
David Lynch and
Mark Frost. The series was originally planned to have nine episodes, however, after re-negotiations between Lynch and Showtime, the episode order was increased, with Lynch confirmed to direct all episodes