The project aims at moving technological frontiers for low-emission combustion of hydrogen to fuel modern gas turbines at high firing temperatures and pressures, beyond the latest state-of-the-art. This will be achieved whilst maintaining high engine performance, efficiency, fuel and load flexibility, without diluents. At the same time, all emission targets set by the Clean Hydrogen JU Strategic Research and Innovation Agenda (SRIA) will be met. The idea is based on a proprietary combustion technology, designated constant pressure sequential combustion (CPSC) already deployed into the GT36 H-class engine (760 MW in combined cycle). The CPSC concept, based on a unique longitudinally staged combustion system, yields the best fuel flexibility and has the greatest potential to achieve the project target of demonstrating stable and clean combustor operation with concentrations of hydrogen admixed with natural gas, up to 100%, at firing temperatures typical of modern H-Class engines. The new, improved combustor design will be fully retrofittable to existing gas turbines, thereby providing opportunities for refurbishing existing assets. The primary objective is to demonstrate the CPSC technology in engine relevant environment (TRL6) in three steps (70, 90 and 100 vol% H2). In this pursuit, a subset of specific performance data (KPIs) will be met within the project timeline and with the planned resources and allocated budget. The project uses state-of-the-art computational tools, analytical modelling, and diagnostic techniques to investigate static and dynamic flame stabilisation. Testing is performed at world-class laboratories in test campaigns at reduced scale and in full size (at atmospheric and pressurised conditions). In preparation for commercialisation, the project will also develop a roadmap towards deployment of the developed system into operation and demonstration into a power plant environment quantifying the valuable contributions to the EU Green Deal.