Today, geopolymer has an important place in producing sustainable alternative products by consuming less energy. This paper researches the elevated-temperature behavior of metazeolite (MZ) and slag (S) based geopolymer composites, reinforced by polyvinyl alcohol fiber (PVA) (at 0.3%, 0.6% and 0.9% by volume), and basalt fiber (B) (at 0.3%, 0.6% and 0.9% by volume). The curing was carried out at room temperature for up to 7 days and then the freeze-thaw test was applied as a curing method for up to 28 days. Slag was used alongside metazeolite to solve the problem of delayed setting time with its high Ca content. After 7 days, the damp environment provided by the freeze-thaw curing ensured the preservation of the compact structure and the continuation of geopolymerization. The resulting geopolymer composites were exposed to temperatures of 250, 500, and 750 degrees C. The flexural and compressive strengths, microstructure (FT-IR, XRD, SEM, TGA-DTA, and micro-CT analyzes), ultrasonic pulse velocity (UPV), visual inspection, and weight-losses of the geopolymers were examined to evaluate their behavior. According to the results, it was observed that geopolymer samples maintained their stability after 750 degrees C. In this way, a sustainable geopolymer composite was produced by using less energy.