The Gold Standard Kart is one of Mario Kart 8's most remarkable unlocks. Not only is it bright and shiny, but it indicates that you're experienced player.
To unlock the Gold Standard Kart, you need to win every cup in Grand Prix mode on both 150cc and Mirror Mode. Only a bronze trophy (1 star) is required for each cup.
Upon earning your last cup you will permanently unlock the Gold Standard Kart for use in single-player and multiplyer.