The official Twitter account for Overlord Season 4 released the first preview trailer and a new key visual. The anime is scheduled for 2022.
The returning staff for the fourth season includes Naoyuki Itou (Hunter × Hunter: Phantom Rouge) as director, Yukie Sugawara (Combatants Will Be Dispatched!) as script supervisor, Satoshi Tasaki (No Game, No Life Zero) as character designer, and so-bin as original character designer. The animation production will be from Madhouse.
The anime’s returning cast includes Satoshi Hino as Ains, Yumi Hara as Albedo, Sumire Uesaka as Shalltear, Emiri Katou as Aura, Yumi Uchiyama as Mare, Masayuki Katou as Demiurge, and Kenta Miyake as Cocytus.
Overlord‘s first season premiered in 2015, while the second and third seasons premiered in 2018. The anime is based on the KADOKAWA-published light novel series by Kugane Maruyama, which began in 2012 and has 14 volumes as of March 2020. The story began as a web novel, first published on Arcadia and later on Shousetsuka ni Narou. Overlord has inspired manga and video games.
Crunchyroll describes the first season as:
When a popular MMORPG is scheduled to be shut down permanently, veteran player Momonga refuses to log out. As NPCs begin to develop personalities and minds of their own he decides to put his skills to use as the game’s new overlord.
Source: Overlord Twitter account