HBO have spent the last few seasons of Game of Thrones trying to keep as much as possible about the series from leaking out, but the series' ability to keep its cast's lips sealed hasn't stopped us learning a lot about seasons six and seven before they aired. That could change for the final season, at least for the ending of the show.
According to statements from HBO programming president Casey Bloys allegedly made during a talk at Bethlehem's Moravian College (via The Morning Call), the show's production team will film multiple endings for the climactic season, so if set reports make their way out you won't be able to tell if it's the actual ending or not:
I know in Game of Thrones, the ending, they're going to shoot multiple versions so that nobody really know what happens. You have to do that on a long show. Because when you're shooting something, people know. So they're going to shoot multiple versions so that there's no real definitive answer until the end.
It's perhaps the ultimate evolution of Game of Thrones' ever-growing fight against spoilers, which in recent years has seen everything from restricting review copies after episodes leaked online, to the world's vaguest episode synopses, to basically not allowing any of the cast to say something that could event be remotely considered as "of note" when talking to the press -- even when it comes to announcing that they're going to be on the show, apparently.
But it's a move that makes sense, as this is the culmination of everything that Game of Thrones will have been building towards for nearly a decade at this point. It getting out months in advance would ruin the moment when it happens on screen. Still, if there are alternate endings actually being filmed, it'd be cool to see those be a) as totally batshit insane and full of fan-theory-nonsense as possible, and b) eventually included on the home release for us to see.