<p>Hastelloy X (HX), a Nickel-based alloy, has garnered significant attention due to its unique combination of mechanical and corrosion properties, making it essential for high-temperature applications. Additive manufacturing (AM) presents a promising approach to address the challenges posed by traditional manufacturing techniques for HX. However, the widespread adoption of AM for HX is hindered by process-induced defects, microstructural variability, and a limited understanding of the relationships among AM parameters, microstructure, and performance. This review consolidates findings from over 200 research studies to present a comprehensive analysis of the current state, challenges, and prospects of AM-fabricated HX. Key topics include the mechanisms of defect formation—especially microcracking—and their impact on the alloy’s performance. Strategies to mitigate defects, including the optimization of alloy composition, process parameters, and the use of post-processing treatments, are critically discussed. Additionally, the microstructural evolution of HX across various AM techniques is examined alongside the influence of post-processing treatments to tailor the microstructure. The paper further explores the performance of AM-fabricated HX, examining its tensile, creep, fatigue, corrosion, and oxidation behaviors. Moreover, the review highlights emerging topics, including lattice structures, powder recycling, productivity, and the design of HX variants for AM. Concluding with the identification of critical research gaps, this study emphasizes the need for a deeper understanding of defect-property correlations, robust standardization, and the development of scalable, cost-effective methods for industrial production. This work aims to guide future research and promote the broader adoption of AM-fabricated HX in advanced engineering applications.</p> Graphical Abstract <p></p>