Additive Manufacturing (AM), and in particular Electron Beam Powder Bed Fusion (EBPBF), has emerged as a transformative route for producing high-performance metallic components with complex geometries and tailored microstructures. Among structural alloys, Ti–6Al–4V remains the benchmark system due to its exceptional strength-to-weight ratio, corrosion resistance, and biocompatibility. However, its widespread application in AM is still limited by the formation of columnar prior-β grains, strong crystallographic texture, and resulting mechanical anisotropy, which originate from steep thermal gradients and directional solidification. This study investigates the processability, microstructural evolution, and structure–property relationships of a Ti–6Al–4V–Cu alloy fabricated via EBPBF with in-situ alloying. The primary objective is to elucidate the coupled interaction between EBPBF thermal conditions and Cu- induced solute effects, and to determine how this interaction governs solidification behavior, phase evolution, and mechanical performance.