The 400 GT replaced the 365 GT4 2+2 model, making its public debut at the 1976 Paris Salon. As with the 365 variant, the model number referred to the swept volume of a single cylinder, whilst the new engine had the same 81mm bore of its predecessor, the stroke was increased to 78mm to give a total capacity of 4823cc. The engine had factory type reference F 101 C 000, and was fitted with two banks of three Weber twin choke side draught 38 DCOE 110-111 M carburettors, with twin coil and rear of engine mounted distributors, to produce a claimed 340 bhp. The engine was mated to a five speed plus reverse gearbox, which transmitted power through a propeller shaft to a limited slip differential, and from there via half shafts to the independently suspended rear wheels with hydraulic self levelling units.
Although the chassis of the 400 series cars were structurally virtually identical to the preceding 365 GT4 2+2 model, there were nominal differences, that resulted in a new factory reference number, F 101 CL 100, for this manual gearbox vesrion. Visually the 400 GT model can be differentiated from its predecessor by a small body colour spoiler on the lower edge of the nose, five bolt fixing for the five spoke alloy wheels instead of the single triple eared spinner, paired circular rear light assemblies, and the disappearance of the "Cavallino Rampante" from the radiator grille. Inside the seat upholstery was made more sumptuous, and the stitch style and pattern altered, along with minor changes to switchgear on the centre console, and a change of style for the door release catch.
The 400 GT continued in production until November 1979, during which time 147 examples were produced in the chassis number range19353 to 28261. As with the 365 GT4 2+2, they were built and fully trimmed at the Pininfarina works in Turin, and then shipped to the Ferrari factory in Maranello for the installation of the mechanical components. Right or left hand drive steering, with power assistance as standard, was available, but as with the other twelve cylinder models of the period, no USA market version was made.