It said they “explore different time periods of George R. R. Martin’s vast and rich universe”, suggesting they take place before or after the events of Game of Thrones as opposed to concurrently.
It usually steers clear of the sequel/spin-off game, but clearly Game of Thrones was just too popular and lucrative.
As recently as SXSW in March they said they would leave the Thrones universe behind after season 8, but now it seems they’ll be serving as executive producers.
Seasons 7 and 8 might spell the end of the main Game of Thrones saga but, in an unusual move from HBO, there is set to be a follow-up series set in its universe.