The present concern in the reduction of CO2 emissions occasioned by heavy duty trucks is leading to a technological evolution, among others, in powertrain electrification. Towards this objective, the EU has funded the project GASTone targeting the development of a new powertrain concept based on the energy recovery from the exhaust gases and kinetic losses in order to make possible the electrification of the main auxiliaries. This new concept will follow a cascade approach in which the exhaust gases energy will be recovered by the integration of an advanced thermoelectric generator followed by a turbo-generator. This system will be combined with a smart kinetic energy recovery device which will recover the energy losses in the deceleration periods of the vehicle. The recovered energy will be used in the electrified auxiliaries. The average performance in a Natural Gas Engine under constant conditions is about 38% (fuel efficiency); with this new concept is expected to rise it by 4% thanks to the engine improvement, by 1% due to the modification of the liquid charge air cooler, by 2% from the reduction of the belt drive, by 1% from the system strategy and management optimization and by 7% from the exhaust heat recovery. The project is in the initial design phase and a dynamic model has been developed to size the different components and to optimize the control strategy in order to minimize the fuel consumption of the engine for a target driving cycle.