I believe it is standard on all vehicles. Here is the press release information on the system:
DRIVING DYNAMICS
The Lexus GS 450h platform has exceptional torsional stiffness and provides an excellent base for the installation of the Lexus Hybrid Drive system, with 50:50 front-to-rear weight distribution.
Positioning the hybrid system’s battery directly above the rear axle aids rear-wheel grip and traction, qualities that are further enhanced by the use of a limited-slip differential.
The Electric Power Steering (EPS) incorporates Variable Gear Ratio Steering (VGRS), which alters the steering gear ratio according to vehicle speed. This demands minimal steering effort at low speeds, with improved feel and feedback as speed increases. The VGRS system is linked to the Adaptive Variable Suspension (AVS) and Lexus’s Vehicle Dynamics Integrated Management (VDIM) system, helping maintain stability and increasing driving reward up the limit of the car’s performance capabilities.
The sophisticated front double wishbone and rear multilink suspension design includes an Adaptive Variable Suspension (AVS) system, with a choice of Sport and Comfort settings. Sport mode increases the difference between inner and outer shock absorber damping through corners to help reduce body roll. At the same time, the Variable Gear Ratio Steering (VGRS) reduces the steering gear ratio and the Electric Power Steering increases steering assist torque to compensate for the increase in steering effort. Ride also benefits from non- linear H ∞ control of all four shocks in response to changes in road surface quality.