This announcement marks a change in the plans of showrunners and executive producers David Benioff and D.B. Weiss, who had previously said they favoured 80 episodes (or eight seasons) to wrap everything up in. The new statements from Benioff, Weiss and HBO seems to be pretty definitive, however.
From David Benioff:
“It feels like this is the midpoint for us. If we’re going to go seven seasons, which is the plan, season 4 is right down the middle, the pivot point. I would say it’s the goal we’ve had from the beginning. It was our unstated goal, because to start on a show and say your goal is seven seasons is the height of lunacy. Once we got to the point where we felt like we’re going to be able to tell this tale to its conclusion, that became [an even clearer] goal. Seven gods, seven kingdoms, seven seasons. It feels right to us.”From HBO Programming President Michael Lombardo:
“I’m expecting to be sitting down with Dan and David to talk season 5 and we’ll talk about how things are looking. We’re all very mindful that they’re having conversations all the time with [author George R.R. Martin]. I think they do feel bullish enough that there’s enough story to deliver through season 7. I hate to sound greedy, but our longest shows have gone 7 or 8 seasons, so seven is a nice long run for us.”Some have interpreted that to mean that eight seasons is still on the table. However, Lombardo's restatement of seven being the plan seems to make that unlikely. Instead, he is referring to the fact that HBO has gone eight seasons or more, but only on (relatively) cheap comedies like Entourage and Curb Your Enthusiasm. In fact, before True Blood no major, big-budget drama show had ever made it to seven seasons before on HBO, with six being the upper limit. The Sopranos was fudged with its final season having twice as many episodes as normal but then split in half to effectively get to seven seasons, but production-wise it was six seasons.
It is possible that something similar could happen here, especially if GoT was moved to a timeslot later in the year (Boardwalk Empire's September slot will be available soon). If GoT's final season was moved to September and aired in two parts, maybe six months apart, that would give the production team the time to film more episodes than normal for the final season. Whether HBO is inclined to do that or willing to spend the money is a different question, of course.
At the moment, however, it appears that Game of Thrones will end in June 2017 after seven seasons and 70 episodes, which puts book author George R.R. Martin and fans of the books in an awkward situation.
As of now, five of seven planned novels in the Song of Ice and Fire series (which Game of Thrones is adapting) have been published. The sixth book, The Winds of Winter, is underway with George's publishers hoping to bring it out before the end of 2015. However, that still leaves the final book, A Dream of Spring, some way off. Bringing it out in less than two years given the time spent on the previous books (at least four and a half years for Winds, over five and a half for A Dance with Dragons and just over five years for A Feast for Crows) would seem unlikely. In a recent interview with Vanity Fair, George suggested that he might still be able to do it - although it would be a "tight," - but this was in the same article where Benioff and Weiss indicated that eight seasons was still doable. Dropping it to seven would appear to make it almost impossible for Martin to stay ahead of the series without a dramatic (and unprecedented in this series) increase in writing speed.
The TV show will remain - at least broadly speaking - faithful to the books even if those books aren't out yet. Martin, Benioff and Weiss sat down at Martin's house in Santa Fe, New Mexico early last year along with script editor/writer Bryan Cogman to drum out story outlines and character arcs so the scriptwriters would be able to plan out the rest of the series.
"Last year we went out to Santa Fe for a week to sit down with him [Martin] and just talk through where things are going, because we don’t know if we are going to catch up and where exactly that would be. If you know the ending, then you can lay the groundwork for it. And so we want to know how everything ends. We want to be able to set things up. So we just sat down with him and literally went through every character."If anything, though, that makes things more difficult for the book fans uninterested in the TV series. If the TV show had a completely different ending, that would be one thing, but if the TV show is going to reveal who gets the Iron Throne, who Jon Snow's parents are and explain the motivations of the Others/White Walkers, and that's the same information as will eventually come out in the books, then it will constitute the biggest and most expensive spoilering of the end of a book in history. Because of GoT's media presence, it may be untenable for people to avoid spoilers for years on end.
As of right now, it appears that Game of Thrones ends in just over three years' time, regardless of if the books come out. What, if anything, GRRM can do about it remains to be seen.