Fraunhofer ISE developed a test procedure for grid-forming inverters in the “GFM Benchmark” project on behalf of the four German transmission system operators. The project assessed devices from several manufacturers and provided an overview of their market readiness while offering input for emerging national and European standards. Tests examined inverter behavior under normal and critical grid conditions, including frequency changes, short circuits, and phase jumps, revealing both similarities and significant differences. Manufacturers received feedback for optimization, and findings were integrated into European standardization efforts, including the VDE FNN note on grid-forming properties. The results also supported preparations for the future market for instantaneous reserve, expected to begin in 2026. ENTSO-E continued work on a European implementation guide to align with national regulations.