The writing of scripts for season six, which will be partially if not largely equivalent to The Winds of Winter
, is now less than a year away. Martin's UK editor said recently that the book itself is "almost certainly years away." Barring an unprecedented increase in his writing speed or a delay for the TV show (which I've heard the producers have already ruled out), the show will overtake the books very soon. I'd say there's some (increasingly slim) chance that The Winds of Winter
will be published before the season based on it airs, but the episodes will almost surely be written and filmed without access to the finished book.