Achieving interoperability in multi-vendor HVDC systems is a key enabler for the efficient integration of offshore wind power into the European grid, supporting the EU’s objective of climate neutrality by 2050. This session will begin with a brief overview of the InterOPERA project's objectives and main challenges. It will then present the real-time demonstrator and outline the proposed approach for defining both overall system and subsystem technical specifications. These specifications translate predefined functional requirements into practical terms, supported by HVDC grid design studies based on generic models. This work highlights the urgent need for a structured process and clear assumption-setting to support effective pre-tender planning studies.