Buick GSX / GSX Stage1 was the optional high performance package available on the GS 455 starting in 1970. The GSX ornamentation package was a $1,100 option on the GS455. The GSX was made to attract attention and to help showroom traffic in an effort to increase sales. The GSX was Buick's answer to Pontiac's GTO Judge and Buick advertised it as "A Brand New Brand Of Buick" and "Another "Light Your Fire Cars From Buick". It was only available with the standard big block 455 engine or the optional Stage 1 engine the first year. It was not a very popular model and not too many people bought them, and only 678 GSX'S were produced in 1970. Just 278 were equipped with the standard 455,with 400 being equipped with the optional Stage 1 performance package. GSX or any GS Stage-1 performance is comparable to that of the 'Hemi' 'Cuda with a much more luxurious car. This is partly due to the light weight of the 455 which is roughly 150 lb (68 kg) less than the Chevrolet 454. The engine's performance also relies on the tremendous torque this engine produces,510 lb/ft at a low 2800 rpm. Quarter mile times in the 13.30s were reported in numerous magazines in 1970. Production dropped in 1971 to only 124,and 44 in 1972. These numbers include the available 350-4 bbl option, the standard 455, and the Stage 1 engines. The 1970 Buick 455 Big block V8 with stage one heads produces around 420 hp and 510 ft·lbf (690 N·m). of torque.

In 1970, the GSX option was available in only two colors, Saturn Yellow and Apollo White (in 1971 and 1972 6 other colors were available for the GSX). All GSXs had the distinctive full body length black stripe that crossed over the standard equipment rear spoiler and was outlined in red pin stripes. A large area of the hood was also black with a hood mounted tachometer (Buick engineers disliked the hood tachometer because it was a Pontiac part) and black front spoiler. Also standard equipment were black bucket seats, floor shifter, wide oval tires, quick ratio steering and anti-sway bars. Some other options were automatic transmission or four speed manual. Four restored versions sold in Barrett-Jackson's 2010 LasVegas auction for as much as $80,000.

After 1970, the 1971 and 1972 GSX became an option that was available on any Gran Sport. Many GSXs survive to this day and can be seen at the Buick Gran Sport Nationals held annually in Bowling Green, KY in the middle of May along with many other examples of '60s, '70s and '80s Buick performance models. Another Buick event is the Buick Performance Group Nationals which is held at National Trail Raceway in Columbus,Ohio during the early month of August.

The GSX and big-block V8 were dropped after 1974. In 1974, the GSX consisted of a trim package on Buick's small, X-bodied Apollo. Three engines were available on the 1974 GSX: the Chevrolet supplied 250 6-cyl.,and two Buick engines:the 350 2 barrel and 350 4 barrel versions.