Unlike in Shelter where room output was boosted by a dweller's SPECIAL (e.g. There is no longer a daily 'evaluation' system. The ability for dwellers to reproduce has been removed. One major change is that the player does not need to feel as if they are babysitting their dwellers as much gone are the happiness, thirst and food meters. The player still plays the role of the overseer of the vault and takes care of its prosperity, but unlike the original game, a plot, online battles, and an overhaul of the dwellers system were added to Fallout Shelter Online. The concept and style of the game are similar to Fallout Shelter, although with added features that resemble a gacha game. Compensation for players of the old version into the new version is available based on criteria such as time played and payments made. Players of the old version can keep their progress by not updating to the new version, though updates for the old version are not planned. However, due to technical difficulties, player progress can not be transferable to the new version. On October 9, 2022, a new updated version of the game was released featuring new gameplay, features, storylines and characters. The game has a Chinese version and a global 'SEA' version which features English.

The game has been translated into English and is available for download online, although it has not been officially released in Western markets. It became available to Indonesia, Malaysia, the Philippines, Singapore, Thailand, South Korea, and Japan under Gaea Mobile on June 1, 2020. It was announced at the end of May 2019, and was first made available to China, Macau, Hong Kong, and Taiwan. It is the sequel to Fallout Shelter and also serves as a prequel to Fallout 4 as well as a sequel to Fallout 3. Fallout Shelter Online (辐射避难所 Online) is a free-to-play mobile game developed by Chinese studio Shengqu Games, published by Bethesda Softworks, and currently distributed by Gaea Mobile.

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