Gastric cancer remains a major global health burden, and accurate staging and response assessment are essential for optimal management. 2-[ 18F]-Fluoro-2-deoxy-D-glucose ([ 18F] FDG) positron emission tomography (PET)/computed tomography (CT) is widely used in oncology. However, it exhibits variable sensitivity in gastric cancer, particularly in poorly cohesive, mucinous, and signet ring cell carcinomas with low glucose metabolism. These limitations have prompted interest in fibroblast activation protein-targeted imaging, which visualizes the tumor stroma rather than the tumor cells. Radiolabeled fibroblast activation protein inhibitors (FAPIs) exhibit high tumor-to-background contrast and consistent uptake across histological subtypes, offering improved lesion detectability even in [ 18F]FDG-negative tumors. This review outlines the evolving role of PET/CT in gastric cancer, with a focus on [ 18F]FDG and FAPI tracers. Comparative evidence indicates that FAPI PET/CT enhances diagnostic accuracy, provides complementary information for evaluating treatment response, and offers potential theranostic applications. Further prospective studies are needed to establish standardized protocols and define the clinical impact of FAPI PET/CT.