Fallout Shelter continues to run in the background even when you're not actively playing. Resources are consumed, production continues, and dwellers can level up or get pregnant. However, incidents (Radroaches, Raiders, etc.) do not occur while offline. This means you can send dwellers on long wasteland explorations or training sessions, then close the game and return later to collect rewards. Be mindful of your resource levels before going offline for extended periods to avoid coming back to a vault in crisis. Use Nuka-Cola Quantum to speed up long tasks if you're impatient, but generally, patience is key to efficient offline progression.
