Tension stiffening describes the capacity of reinforced concrete to carry tensile forces between cracks. Typically, for design purposes, regular concrete is not considered capable of providing any tensile resistance. However, the use of composite materials with enhanced mechanical properties, such as ultra-high-performance concrete (UHPC), significantly enhances the tensile resistance and the overall member stiffness. This paper experimentally evaluates the tension stiffening response and cracking behavior of UHPC members reinforced with glass fiber-reinforced polymer (GFRP) bars, both ribbed and sand-coated, under axial tension. Additionally, UHPC members reinforced with steel and GFRP rebars were assessed and compared. Fiber-optic sensors were used to measure strain distributions along the specimens and Digital Image Correlation (DIC) was employed to determine crack evolution and widths. Results show that the UHPC members exhibit higher tension stiffening when compared with GFRP bars in normal concrete. This increased stiffening is attributed to the reinforcing effects of steel fibers in the UHPC, which bridge cracks and enhance the tension stiffening behavior. The influence of bar surface had a small impact on the tension stiffening response on normal concrete members. For UHPC members, the type of axial reinforcement used, whether steel or GFRP, did not have an impact on the concrete behavior. Additionally, a simplified approach to predict UHPC post cracking behavior for axially reinforced members is presented. Understanding the effects of tension stiffening is important for assessing post cracking serviceability behavior of UHPC structures and developing proper constitutive models for UHPC.