He said as much while promoting his newest film Shot Caller in an interview with Collider, revealing, "I knew what was going to happen for the first three seasons. After that, it's been a season at a time. You get the scripts a month before we start shooting, or six weeks, and then you know what's going to happen that season. But, I don't know what's going to happen next season. We go back in October, so maybe in the next few weeks, we'll get the scripts and I'll find out. I'm very curious."
He might not know what we should expect from the final episodes of Game of Thrones, but his words do assure us that Jaime Lannister will at least make it through Season 7 somehow — even though he's been pretty heavily imperiled this season, courtesy of the loot train battle and his brush with subterfuge of his sister-slash-lover-slash-Queen Cersei (Lena Headey).
The October start date is a bit later than previous seasons have started — with ordinary production schedules kicking off in late August and running through to February. However, Season 8 is only expected to feature six episodes, as opposed to the usual 10 and this season's eight, so the schedule's impact on the new season's as-yet-unannounced premiere date is unknown at this time.
Perhaps there is a need for more snowy horizons this time around, since, you know, winter is here now.
Game of Thrones airs Sundays on HBO at 9/8c.