[ANIME SPOILERS] Special episode after season 2? 24.06.2017?

Hey, it's not really anime spoiler, but... will there be a special episode week after finale?

Sources:

1. https://anidb.net/perl-bin/animedb.pl?show=ep&eid=188215
2. http://shingeki.tv/news/archives/3017 [I don't really know what it says though :P)

On Polish site I've read that it'll be based on manga. How situation looked like with previous special episodes? Are there parts of manga not covered yet that happend till newest episode?