This thing was told to me as having the biggest footprint of any citadel model. It is a dual kit, making either the Necron Tesseract Vault or the Necron Obelisk. I believe the Tesseract Vault is the one that we have all been seeing, while the Obelisk looks like a closed up version of the Tesseract Vault.
Please remember that these are rumors, and until something official is released, salt is always required.
I have a lot less information on this beast of a model, but here it goes.
Tesseract Vault
Is a war machine containing the godlike powers of a Necron Transendant C'tan, who is protected by the Vault
Necron Obelisk
Is a weapon deadly to enemy flyers and skimmers.
If built using the Obelisk option, you can make a separate Transcendant C'tan