It will be mostly compatible. You will need to subscribe to OnConnect, OnDisconnect etc other type of events that used to be broadcast before. Also, server-wide broadcasts won't work anymore in TNet 3, if you've used them. You'll need to join a common secondary channel and communicate through it instead for when you need cross-channel communication (example: chat). RCCs no longer need to be registered -- TNet 3 will find them automatically. Pretty sure TNet will tell you about the rest, or you can just gleam it from the tutorials.