Absolutely nothing has been confirmed yet. Otaku House had this joke on Apri 1st where they said season 2 would start airing in July.
Shingeki no Kyoujin season 2 is not on the Summer chart, nor the Fall chart. Not even on the To-Be-Added chart where series that might start airing a year from now are listed.
Oh, they are. But they are also unimaginable shy.
Spoiler