Europe is fielding two sixth‑generation fighter families, the UK‑Italy‑Japan Global Combat Air Programme (GCAP) and the Franco‑German‑Spanish Future Combat Air System (FCAS), to reclaim strategic autonomy following F‑35 kill‑switch and data-sharing concerns. This InfoFlash frames interoperability as the decisive variable, defines the pan‑European combat cloud, and maps overlaps between GCAP, FCAS, and enabling standards such as Link16, ESSOR, EICACS and EPIIC. Making the two projects interoperable would allow Europe to fuse compress decision cycles and deny hostile vetoes over its airpower. Risks of fragmentation emerge if divergent architectures, EU–UK/Japan divides, or legacy dependencies persist. Recommendations call for a NATO‑anchored Combat Cloud Waveform task force, a federated digital‑twin lab chain, and a GCAP‑FCAS board to translate study outputs into flight‑verified standards before 2030. Achieving interoperability by design would secure European sovereignty and coalition effectiveness.