From Halopedia, the Halo wiki
The Brute Tank is a cut vehicle, intended for use by the Covenant in Halo Wars, specifically for the Brute Leader. It's intended role is similar of the Wraith's and a replacement for the brutes.
A Brute Tank (top-left) alongside several other early renders of Covenant vehicles.
A pair of Brute Tanks (lower-left) alongside other Covenant vehicles.