<p>The high-temperature oxidation behavior of Haynes 214 alloy with different yttrium contents (0.0016 ~ 0.089 wt.%) at 950&#xa0;°C was investigated. The results revealed a non-monotonic dependence of oxidation resistance on Y content, with an optimum at approximately 0.012 wt.%. At this optimal composition, Y increases the alloy lattice constant, which enhances the diffusion of Al to the surface. This ensures the formation of a continuous and dense Al₂O₃-based protective scale. In contrast, at Y contents below this optimum, insufficient Al diffusion leads to a non-protective oxide scale prone to spallation. When Y exceeds its solid solubility limit, excess Y precipitates as Ni₅Y phases. These precipitates act as fixed short-circuit paths for oxygen during oxidation, initiating internal oxidation and ultimately degrading the protective scale. Therefore, the optimal Y window for Haynes 214 is defined by a balance between enhanced Al diffusion and the avoidance of detrimental Ni₅Y precipitation.</p>