As already earlier indicated by their used tags on Bilibili, Famitsu‘s two page feature on Arknights: Endfield confirms that the game will be free to start with in-app purchases. Prior to the official teaser announcements, there were numerous “leaks” and rumours swirling around claiming the game to be a premium title and / or a third-person shooter, among other things.
The Famitsu feature also indicates that despite bearing the “Arknights” name, it is not a sequel to the original game, but does not directly state if the game’s timeline is somehow running concurrently with the tower defense title, or the possibility that it could be a prequel. All that we can really say for certain that it takes place in the same universe, besides being a “3D RPG with strategic elements” slated for release for mobile and PC.
Hypergryph are presently recruiting, with positions available across a variety of disciplines, some specifically for Endfield as well. Arknights will be having its third anniversary (China release) stream on 23 April 2022, so free up your time to catch it and see if there’s any further Endfield teasers. Considering its status of being “early in development”, tangible news sounds unlikely, but stay tuned. You can check out the English Twitter account and the official website in the mean time.