How does Unreal Engine 5 manage to stream such amounts of data? The answer is World Partition.
It doesn't require artists to build maps as a series of streaming levels but rather takes a single map as one large world and breaks it automatically into smaller streamable cells on a grid. These cells can then be loaded or unloaded to save resources.
Please note that changes are tracked at the actor level, not the map level allowing different artists to work on different actors on the same map. Artists can tweak lighting, assets, and other details simultaneously.
As for the performance, World Partition makes sure that only specific cells in a user-defined radio from a player are loaded. New cells are streamed in when you move while others are replaced by their lower resolution level of detail version. The cell size and loading radius are fully configurable to match the project's needs.
Learn more about the engine, available in early access starting today, here.