The G-STEEL GST-B400 model has a new improved design made possible by a thin module and carbon core guard structure. Power consumption has also been significantly reduced. The carbon core guard structure of this model helps to make it the thinnest of the G-STEEL Series (as of Apr 2021) while maintaining a high level of impact resistance. The thickness from the back cover to the bezel top is only 12.9 mm, which is more than one millimeter less than the GST-B100 model. The top bezel has been given five different finishes, while the middle bezel has been given four different finishes, which creates an elegant effect and changes the appearance of the texture of the metal depending on the viewing angle.