Injection molding using inserts from vat polymerization, an additive manufacturing technology, has been investigated for pilot production and rapid prototyping purposes throughout the past years. A standard mold is equipped with additively manufactured inserts in a rectangular shape of (20 x 20 x 2.7) mm3 produced with vat photo polymerization. While the lifetime compared to conventional materials such as brass, steel, and aluminum, is reduced, the prototyping and design phase can be shortened significantly by using flexible and cost-effective additive manufacturing technologies. Higher manufacturing volume still exceed the capability of additively manufactured inserts, which are overruled by the stronger performance of less-flexible but mechanically advanced materials. In this contribution, the internal structure of a high-performing, fiber-reinforced injection molding insert has been analyzed. The insert reached a statistically proven and reproducible lifetime of 4,500 shots, which significantly outperforms any other previously published additively manufactured inserts. Computer tomography, tensile tests and life cycle analysis have been performed in order to provide an understanding of the internal structure of fiber-reinforced, additively manufactured injection molding inserts. This paper therefore contributes to a further understanding of injection molding inserts produced by additive manufacturing, which come with major advances in flexibility, cost efficiency, cycle time, and micro-features. The enhanced lifetime reduces the production cost share as well as the workforce required to change defect inserts. Moreover, the suitability for thermally more pretentious materials is increased.