The Casio G-SHOCK G-STEEL GST-B400-1AWC is a solar-powered, shock-resistant analog-digital watch built around the brand's Carbon Core Guard structure — a carbon fiber-reinforced resin case that delivers exceptional durability at a remarkably slim 12.9 mm profile, the slimmest in the G-STEEL lineup. The case measures 46.6 × 49.6 × 12.9 mm and weighs just 80 grams, combining a stainless steel bezel with a black resin band. The dial features a clean black face with analog hour and minute hands and an integrated digital display showing time, date, day, and secondary information.

Powered by Casio's Tough Solar technology, the watch charges continuously from any light source and operates for approximately 7 months on a full charge without additional light exposure, or up to 18 months in power-save storage mode. Bluetooth connectivity pairs with the CASIO WATCHES smartphone app for automatic time synchronization up to four times daily, world time access for over 300 cities, reminder settings, phone finder, and timer and alarm management via smartphone. World time covers 38 time zones with daylight saving time support.

Features include a 1/100-second stopwatch with lap and split time, a 60-minute countdown timer, five daily alarms with an hourly time signal, a full auto-calendar accurate to the year 2099, and a double LED Super Illuminator backlight with selectable 1.5- or 3-second illumination duration. The watch is water resistant to 200 meters (20 bar) and carries G-SHOCK's standard shock-resistant construction with buffering components mounted between the upper and lower bezels. The mineral glass crystal is treated with Neobrite luminescent coating on the hands for readability in low-light conditions. A hand-shift feature moves the analog hands out of the way for an unobstructed view of the digital display.