FLEX4H2 aims to develop a fuel-flexible combustion system and will contribute to the EU Green Deal towards decarbonisation of the electric power sector.The aforementioned goal translates into the project’s main objective – to design, develop and validate a safe, efficient and highly fuel-flexible combustion system capable of operating with any concentration of hydrogen blend up to 100% H2. Crucially, this objective will be pursued at the most challenging hydrogen combustion conditions, i.e., at H-Class operating temperatures, required for highest cycle efficiency, while still meeting emission targets without any use of diluents. The design of the combustor will be based on Ansaldo Energia’s Constant Pressure Sequential Combustion technology (CPSC) and will be demonstrated in a stepwise approach, at full gas turbine operating conditions (TRL6).