Unreal Engine replication
Epic's own account of how Unreal does multiplayer. The engine picks one of netcode's three families and does not offer the others: client-server with an authoritative server, where "the server, as the host of the game, holds the one, true, authoritative game state." Clients send commands; the server runs the gameplay logic and decides what happened.
The unit of replication is the Actor
An Actor is the class the network layer knows about. When an authoritative replicated Actor spawns on the server, the engine "automatically generates remote proxies of itself on all connected clients." That spawn-and-proxy step is the whole model in one sentence: a client never owns the object, it holds a shadow of one.
Two ways to move data onto those proxies.
Replicated properties. Mark a property as replicated and it syncs from the authoritative Actor to its proxies whenever the value changes. The RepNotify variant calls a function on the client when the value lands, and Epic tells developers to prefer it over an RPC where both would work, because it is cheaper.
RPCs, in three flavours by where they run: Server (only on the server), Client (only on the owning client), Multicast (on everyone). Each can be reliable — delivery guaranteed, at a cost — or unreliable.
What the engine does when the link is too small
Two mechanisms, both automatic and both worth knowing about because they decide what a player does not see. Relevancy decides whether an Actor matters to a particular connection at all. Net priority ranks the ones that do, so that when bandwidth runs out the engine drops the least important rather than the last in the list. The documentation also names a Replication Graph and an Iris replication system as the paths for taking that decision away from the defaults.
Two ways to host
A dedicated server runs no local player and is what Epic points at for competitive and large-scale games. A listen server is a player hosting from inside their own session, which Epic scopes to casual co-op. The distinction is not a deployment detail: the listen-server host has zero latency to the authority and everyone else does not.
Against the other two engines
This is the most prescriptive of the three stacks read on 2026-08-25. Unreal does not ask the developer to pick a topology — there is one, it is server-authoritative, and the tuning surface is relevancy and priority rather than authority. Compare unity-netcode-gameobjects, which ships two topologies and makes the choice a project decision, and godot-multiplayer-api, which hands over a peer abstraction and a default the developer is free to reassign per node.
Related
netcode · unity-netcode-gameobjects · godot-multiplayer-api · unreal-engine · ggpo · game-networking-fiedler