Phase-pure antiperovskite nitrides (A3XN; A = Co, Ni; X = Zn, In, Sn) synthesized via a melamine method were evaluated as cost-effective, high-performance hydrogen evolution reaction (HER) electrocatalysts. Initial tests in 1 M NaOH electrolyte revealed limited activity, significantly enhanced by reductive electrochemical cycling, attributed to the in situ formation of catalytically active zero-valent Co0 and Ni0 surface species. Comparative studies of isostructural Fe-based nitrides confirmed that these metallic A-site species constitute the active sites. Accelerated stability tests (95 °C, 10 M NaOH) identified Co3ZnN and Ni3ZnN as particularly robust, maintaining intact antiperovskite structures and high catalytic activity (>70 mA cm–2 after 210 h). Partial substitution (Zn for In) further improved stability, notably for Ni3Zn0.25In0.75N. This study highlights the crucial role of compositional tuning and surface activation in optimizing HER performance, emphasizing that systematic stability assessments under industrially relevant conditions (high temperature, concentrated electrolyte) are essential. Antiperovskite nitrides thus offer promising avenues for scalable, green hydrogen production technologies.