Using natural gas in large bore engines reduces carbon dioxide emissions by up to 25% at a lower fuel cost than diesel engines. In demanding applications with highly transient operating profiles, however, premix gas engines have disadvantages compared to diesel engines because of the potential for knocking and misfire to occur. Operating a gas engine using the diesel cycle requires high gas injection pressures. Furthermore, a source of ignition is needed due to the high autoignition temperature of methane. State-of-the-art solutions inject a small quantity of diesel fuel before introducing the natural gas. One monofuel alternative ignites the gas jets with flame torches that originate in a prechamber. This paper presents the simulation based development of a prechamber ignited high pressure direct injection (HPDI) gas combustion concept and subsequent experimental validation. After the most promising arrangement of the prechamber and the high pressure gas injector was selected, the main focus was on optimizing the prechamber geometry and prechamber operating conditions. 3D simulation models were set up to determine the optimal geometry of the prechamber combustion volume as well as the number, size and shape of the channels connecting the prechamber to the main combustion chamber. The prechamber optimization targets include trapped fuel mass and mixture quality in the prechamber. Combustion of the gas jets was predicted with the ECFM-3Z model under the assumption of ideal injection rates. The results of the 3D simulation were transferred to a 1D multicylinder engine model to generate statements about engine efficiency and to provide boundary conditions for experimental validation. The best prechamber design was selected for prototype manufacturing and testing on the single cylinder research engine. After the prechamber concept is validated, it will be possible to make initial statements on the feasibility of the overall combustion concept for large bore engines.