It was announced by author Timothy Zahn during the Lucasfilm publishing panel at NYCC 2017 that he will be releasing a sequel to his Thrawn novel, which arrived on bookstore shelves earlier this year. The sequel, titled Thrawn: Alliances, is slated to land sometime during the summer of 2018, though Zahn revealed during the panel that he has already submitted the final copy of the book to Del Rey.
The other big news pertaining to this sequel novel is that it will feature the dark lord of the Sith himself, Darth Vader, in a prominent capacity. What that capacity will be remains to be known, but just the thought of Thrawn and Vader together should make for one hell of a storytelling adventure.
— Star Wars Books (@DelReyStarWars) October 6, 2017