Efficient generation of DC spin-polarized currents via light is a promising route toward ultrafast spintronics, yet remains challenging. Here, we show that altermagnets, a class of antiferromagnets with symmetry-driven spin splitting, can generate DC spin currents via the nonlinear spin Hall effect. Using a three-dimensional Hubbard model, we identify the Berry curvature dipole as the dominant source of the nonlinear response, while the first-order quantum-metric-like term yields only ac spin currents. The contribution from the Berry connection polarizability is found to vanish in the absence of spin-orbit coupling. A comprehensive symmetry analysis of all noncentrosymmetric spin point groups, supported by first-principles calculations for ${\mathrm{CuFeS}}_2$, establishes altermagnets as a robust platform for pure spin-current generation. The predicted second-order spin-current conductivity reaches the ${\mathrm{mA}/\mathrm{V}}^2$ range, demonstrating experimental feasibility and highlighting the promise of altermagnets for ultrafast spintronics, including terahertz applications.

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• Electrical properties
• Altermagnets
• Density functional calculations
• Terahertz techniques