Six episodes first week, eight part Islands special next week.
http://adventuretime.wikia.com/wiki/List_of_episodes#Season_8:_2017
http://www.gizmodo.com.au/2016/12/adventure-time-will-explore-finn-the-humans-past-in-a-new-eight-part-special/
Like the S7 finale, CN hasn't been promoting this much. I hope this doesn't lead to the show getting cancelled prematurely.
"DO NOT WRECK THIS GIGANTIC DOOM."
http://astrolupine.tumblr.com
They've already announced that season 9 is the last. It's not getting canceled before then.
shareThe first four episodes have aired and are available online, but CN have mangled the episode numbering!
http://www.cartoonnetwork.com/video/adventuretime/episodes/index.html
All 8 episodes of Islands are on pirate sites, but I don't know where they came from.