Small-molecular fibroblast activation protein inhibitor (FAPI)-based tracer have been shown to be promising Positron Emission Tomography (PET) ⁶⁸Ga-labeled radiopharmaceuticals to image a variety of tumors including pancreatic, breast, and colorectal cancers, among others. In this study, we developed a novel ¹⁸F-labeled FAPI derivative. [¹⁸F]6 was labeled using a synthon approach based on the tetrazine ligation. It showed subnanomolar affinity for the FAP protein and a good selectivity profile against known off-target proteases. Small animal PET studies revealed high tumor uptake and good target-to-background ratios. [¹⁸F]6 was excreted via the liver. Overall, [¹⁸F]6 showed promising characteristics to be used as a PET tracer and could serve as a lead for further development of halogen-based theranostic FAPI radiopharmaceuticals.