We had four scripts in development when I arrived in LA last week, but by the time I left we had five. We have added a fifth writer to the original four. No, I will not reveal the name here. HBO announced the names of the first four, and will no doubt announce the fifth as well, once his deal has closed.
Martin further notes that the five successor shows are, strictly speaking, not spinoffs but prequels:
For what it’s worth, I don’t especially like the term “spinoff,” and I don’t think it really applies to these new projects. What we’re talking about are new stories set in the “secondary universe” (to borrow Tolkien’s term) of Westeros and the world beyond, the world I created for A SONG OF ICE AND FIRE. It is a world, and a pretty big one, and if there were eight million stories in the naked city back in the 50s, just think how many more there are in an entire world, and one with thousands of years of recorded history.
None of these new shows will be ‘spinning off’ from GOT in the traditional sense. We are not talking Joey or AfterMASH or even Frazier or Lou Grant, where characters from one show continue on to another. So all of you who were hoping for the further adventures of Hot Pie are doomed to disappointment. Every one of the concepts under discussion is a prequel, rather than a sequel. Some may not even be set on Westeros. Rather than ‘spinoff’ or ‘prequel,’ however, I prefer the term ‘successor show.’ That’s what I’ve been calling them.