The official website for the Sword Art Online Alicization anime has now updated to reveal when its “final season” will premiere. According to the website, the series will premiere on 25th April 2020. It also features a brand new key visual for the new season as well:
From the key visual, it looks like it will really be intense, and the other SAO characters like Leafa and Sinon are finally joining in.
Previously, the light novels’ editor, Kazuma Miki, revealed that the anime will cover the entire Alicization arc. The arc itself lasts for a whopping 11 volumes, from Volume 9, all the way to volume 19. This makes the arc longer than all of SAO’s previous story arcs combined. Expect the staff to reveal more details soon.
Source: SAO Alicization official Website