It was announced on Monday by the official Facebook page of Toonami that they will be officially airing Attack on Titan Season 3 on August 18. It will premiere in Japan on July 22.
A world premiere for the season’s first episode happened during Anime Expo last July 8. Last week, a screening event of the first episode was also held in US and Canada last week by Funimation.
Aside from watching the anime in Toonami, Hulu, Funimation, and Crunchyroll will be airing the anime same day as Japan (with Subtitles) while Funimation will also be streaming it in English Dub.
Source: Toonami’s Official Facebook Page and Anime News Network