Usually Game of Thrones has five directors per season, with each directing two episodes, but next year there will only be four. HBO hasn't confirmed that Season 7 will be shorter, but showrunners D.B. Weiss and David Benioff have been saying that there are only approximately 13 episodes left in total, and fewer directors could indicate fewer episodes per season.
The directors are:
-Alan Taylor, who will be directing Game of Thrones for the first time since 2012. He was pivotal during Game of Thrones' early years, directing Season 1's "Baelor," a.k.a. "the one where Ned Stark gets his head cut off," as well as four eps in Season 2. He then left Westeros for Hollywood, directing Thor: The Dark World and Terminator: Genisys.
-Jeremy Podeswa, another GoT vet who directed Season 5's infamous "Unbowed, Unbent, Unbroken," for which he received an Emmy nomination. He directed the Season 6 premiere, as well as "Home," a.k.a. "the one where Jon Snow comes back to life."
-Matt Shakman, who will be making his Game of Thrones debut. He's previously directed episodes of Mad Men, Fargo and The Good Wife, although he's best known for directing 39 episodes of It's Always Sunny In Philadelphia. It'll be interesting to see what he does.
Notably absent is Miguel Sapochnik, who has directed some of the series' finest episodes, including the last two of Season 6; and David Nutter, who directed the Season 5 finale "Mother's Mercy," my personal pick for the best episode of the series.
In semi-related news, it was also officially confirmed that Rhaegar Targaryen is Jon Snow's father.