Since version 1.5.0, Coffee GB has supported rollback-based netplay. This unique feature provides stable netplay even over slow internet connections, unlike other emulators that typically only support local play or fast LAN connections. To enable rollback-based netplay, Coffee GB emulates two Game Boys: one for the local player and a second, invisible one that receives button presses from the remote player.
Coffee GB 1.6.0 improves the user experience for netplay. Previously, establishing a connection between two emulators would stop the emulation, requiring both players to load the game to restart. With version 1.6.0, the connection is established dynamically without stopping the running game. To achieve this, a snapshot of the current game state is taken and transmitted over the network to the other emulator, so the "invisible" Game Boy can run it.