The fourth-generation Lexus GS sedan is a quiet executive car with gasoline and hybrid choices. You can match a drivetrain and a named equipment package to how you actually use the car.
A Lexus GS engine here is gasoline or hybrid. The 3.5 AT sedan pairs an automatic with all-wheel drive, the 3.5 CVT hybrid a variable transmission with rear-wheel drive, and the 2.5 AT a rear-drive automatic. These powertrain examples are not the full lineup.
Lexus GS trim levels on the 2.5 AT rear-drive gasoline sedan include 25 Anniversary Edition Luxury and 25 Anniversary Edition Premium. Those packages share the same engine and automatic; they differ in equipment, not in the mechanical version. Treat each name as its own kit rather than a separate car.