The photo was of one of the prototype GVT (Gefechtsversuchsträger). Generally falling under this title there were (at least) two further definitions; VT 1-1 (twin 105mm guns), and VT 1-2 (twin 120mm guns). This one is VT 1-2. It is often mistakenly referred to as a Kampfpanzer 3 or a Leopard 3.
This is again the same pointless debate on obscure experimental designations as in case of Bren prototype. Various sources give various designations. This is what Munster tank museum has to say on topic: