Introducing new color variations to the lineup of slim G-STEEL GST-B400 models with new, improved designs made possible by a thin module and carbon core guard structure. The GST-B400AD comes with a black ion-plated (IP) bezel combined with a vapor deposition dial in G-SHOCK red.

The GST-B400 is made possible by even further miniaturization of its parts and thinning of its modules without sacrificing any Bluetooth or solar function. Power consumption has also been significantly reduced.

In addition, 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.
In terms of design, the number of button guards has been reduced as much as possible, enabling the use of large stainless steel buttons that are slim yet easy to operate.

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.
 
Case / bezel material: Resin / Stainless steel
Resin Band
Mineral Glass
Neobrite
Shock Resistant
Carbon Core Guard structure
200-meter water resistance
Shock resistant (G-SHOCK)
Tough Solar (Solar powered)
Double LED light
LED light for the face (Super illuminator, selectable illumination duration (1.5 seconds or 3 seconds), afterglow)
LED backlight for the digital display (Super illuminator, selectable illumination duration (1.5 seconds or 3 seconds),afterglow)
Mobile link (Wireless linking using Bluetooth®）
Hand shift feature (Hands move out of the way to provide an unobstructed view of digital display contents)
World time
38 time zones (38 cities + coordinated universal time), city code display, city name display, daylight saving on/off, auto summer time (DST) switching, Home city/World time city swapping
1/100-second stopwatch
Measuring capacity: 00'00''00~59'59''99 (for the first 60 minutes)
1:00'00~23:59'59 (after 60 minutes)
Measuring unit: 1/100 second (for the first 60 minutes)
1 second (after 60 minutes)
Measuring modes: Elapsed time, lap/split time
Countdown timer
Measuring unit: 1 second
Countdown range: 60 minutes
Countdown start time setting range: 1 second to 60 minutes (1-second increments and 1-minute increments)
5 daily alarms
Hourly time signal
Battery level indicator
Power Saving (display goes blank to save power when the watch is left in the dark)
Full auto-calendar (to year 2099)
12/24-hour format
Button operation tone on/off
Date/month display swapping
Day display (days of the week selectable in six languages)
Regular timekeeping
Analog: 2 hands (Hour, minute (hand moves every 20 seconds))
1 dial (battery level, mode)
Digital: Hour, minute, second, pm, month, date, day
Accuracy: ±15 seconds per month (with no mobile link function)
Approx. battery operating time:
7 months on rechargeable battery (operation period with normal use without exposure to light after charge)
18 months on rechargeable battery (operation period when stored in total darkness with the power save function on after full charge)
Size of case : 46.6×49.6×12.9mm
Total weight : 80g