FAPI-X5 is an inhibitor of fibroblast activation protein (FAP). It binds to the catalytic domain of FAP, forming hydrogen bonds and engaging in π-π stacking with key active residues, resulting in functional inhibition. FAPI-X5 exhibits albumin-binding activity, which extends its systemic circulation half-life. It shows cytostatic effects on glioblastoma cells, slowing tumor growth without causing tumor regression. When labeled with [^68Ga], FAPI-X5 serves as a PET tracer, displaying rapid tumor uptake and high-contrast imaging in glioblastoma-bearing mice. Additionally, when labeled with [^177Lu] or [^47Sc], it acts as a targeted radionuclide therapeutic, offering prolonged tumor retention. FAPI-X5 is applicable in glioblastoma research.