Abstract Metallic materials for aerospace and liquid hydrogen technologies need to maintain high strength and ductility under cryogenic conditions. However, conventional strengthening strategies typically increase defect density and promote strain localization, resulting in a strength–ductility trade‐off. This limitation becomes more critical at ultralow temperatures, where it facilitates discontinuous plastic flow and abrupt stress drops, substantially increasing the risk of premature failure. Here, a Co 36 Ni 46 Mo 11 Al 7 medium‐entropy is developed, exhibiting an exceptional combination of tensile strength (2.1 GPa), high ductility (48%), and remarkably low stress drops of ≈99 MPa at 4.2 K. This balance is enabled by two key mechanisms: enhanced lattice friction through compositional tuning and the introduction of coherent L1 2 nanoprecipitates. These features effectively impede dislocation motion while promoting Hirth lock formation, thereby suppressing strain localization. Crucially, cryogenic loading–unloading–reloading tests, rarely performed at 4.2 K, reveal low back stress, directly indicating minimal dislocation accumulation despite the high strength. The findings highlight how dislocation–precipitate interactions can decouple strength from back stress accumulation, enabling a rare combination of ultrahigh strength and suppressed discontinuous plastic flow. This approach establishes a robust alloy design strategy for overcoming the long‐standing conflict between strength, ductility, and mechanical stability in cryogenic environments.

This study introduces a method that is applicable across various powder materials to predict process conditions that yield a product with a relative density greater than 98% by laser powder bed fusion. We develop an XGBoost model using a dataset comprising material properties of powder and process conditions, and its output, relative density, undergoes a transformation using a sigmoid function to increase accuracy. We deeply examine the relationships between input features and the target value using Shapley additive explanations. Experimental validation with stainless steel 316 L, AlSi10Mg, and Fe60Co15Ni15Cr10 medium entropy alloy powders verifies the method's reproducibility and transferability. This research contributes to laser powder bed fusion additive manufacturing by offering a universally applicable strategy to optimize process conditions.