I’ve seen people here saying that the developers want to add the behemots on a future updadte.
My guess is that if they want to add it the to the game, they will do this on DLC 3 - Festering Skies.
The skies darken with alien vessels, and Phoenix Point must rise to the challenge. An all-new interception mode, inspired by the original X-COM, lets players build and upgrade their own aircraft, fight aliens in the skies, and harvest tech from downed alien vessels. Festering Skies boasts an entirely new play style, new mission types, new vehicles, and much more.
https://www.epicgames.com/store/en-US/product/phoenix-point/festering-skies