Permeation of hydrogen isotopes from the upstream pressure through a membrane into high vacuum at elevated temperatures is a challenging task for vacuum technology, especially when very low fluxes must be determined. Geometrical and mechanical constraints set an engineering issue since the ultimate tightness of the seals at high temperature must be preserved. Recording the steady permeation flux and its transients requires high sensitivity and stability of the gauges. It is anyhow far more challenging to suppress the hydrogen background outgassing flux to the level when it represents only a fraction of the permeation flux. The authors present an innovative permeation cell design that results in efficient hydrogen background suppression. When implemented in an all-metal UHV system, low permeation flux density of hydrogen down to j∼10−9 mbar L/(cm2 s) could be measured on disk-shaped membranes having an area of 8.4 cm2.