After the airing of Episode 59 of Attack on Titan (Shingeki no Kyojin), it was announced that a fourth and final season of the anime will begin airing in October 2020. Hajime Isayama previously announced that the manga was coming to its conclusion a while back and with the anime airing at the end of next year, it gives Isayama plenty of time to wrap things up. It could also be a situation where the manga and the anime end at the same time, which is something that has been done in the past with other series.
The third season concluded with Eren and co. fulfilling Armin’s promise from the beginning of the series as well as revealing the truth about the world. This means we will see the culmination of that truth in the final season as well as the aftermath and epilogue.
A promotional video for the final season is streaming online which you can view below: