A commercially available compact Josephson voltage standard N4-21 based on high-temperature superconductor Josephson junctions with dry nitrogen temperature cooling is presented. The cryocooler unit of the voltage standard including the cryogenic system and the high-temperature superconductivity Josephson array chip is described. The measured relative standard uncertainties between output voltages of N4-21 and the primary state voltage standard of Russia are only a few parts in 10⁸. Such low uncertainties are sufficient for the application of voltage standard N4-21 in the highest-level metrology. The implementation of the link between Josephson junctions and Zener diodes largely eliminates the uncertainty contributions associated with Zeners nonlinear drift, environmental effects, and the impact due to shipping.