The development of very high bypass ratio (VHBR) aero-engines can contribute to fulfilling the goals of the Sustainable and Green Engines (SAGE) program. The potential environmental benefits of the new aero-engine concept require increased speed and loading capabilities as compared to today's solutions. This paper describes the development of an advanced temperature-resistant, corrosion-tolerant steel for hybrid bearing rings for aero-engine applications. The target was for an increase in the hybrid bearing load capacity by 15% plus an increase of 25% in the rotation speed capability. In order to achieve the load capacity target, the steel rings of the hybrid bearing needed to be improved in terms of hardness, specifically hot hardness. The composition of Pyrowear® 675 was taken as a basis for the development and the alloying philosophy centered around the use of cobalt because of its beneficial effects on hot hardness. A series of small-scale test melts were made with the initial compositions being modeled using Thermo-Calc software. The heat treatment response of the initial melts was used to define further test melts to refine the composition to a final target composition for an industrial 16-ton Vacuum Induction Melting–Vacuum Arc Remelting (VIM/VAR) melt. This patented novel composition was produced by a commercial steelmaker in the first half of 2018. The paper will describe how the final alloy composition was developed by combining modeling with experimentation. The next steps toward implementation of the concept will be outlined.