Unreal Engine Level Instancing guide: Manage reusable scenes

Epic Games’ Unreal Engine documentation describes Level Instancing as a level-editing workflow that groups Actors and makes them reusable throughout a project. This guide covers the steps for creating and editing repeating buildings or static mesh groups in architectural visualization and design scenes, as well as understanding World Partition behavior. Since the source documentation does not specify a particular Unreal Engine version, this guide is limited to the interface and features described in the documentation.

The difference between Level Instance and Packed Level Blueprint

A Level Instance groups multiple Actors in a single sublevel. The resulting level can be placed at different points in a project; when an edit is committed on one instance, it is applied to the other copies of that instance as well. This makes it possible to treat buildings or visual arrangements reused in different parts of a scene as a shared unit.

Packed Level Blueprint serves a different purpose: it combines static meshes in a Blueprint Actor. Epic Games’ documentation says this structure is optimized for rendering and recommends it for dense visual arrangements such as static buildings. So, decide upfront whether you need an editable collection of Actors or a packed structure made up of static meshes.

Creating an instance from a group of Actors

1. Select the Actors you want to use together in the Viewport or Outliner. This selection determines the contents of the instance you create.

2. Right-click one of the selected Actors. For a Level Instance, choose Level › Create Level Instance; for a Packed Level Blueprint, choose Level › Create Packed Level Actor.

3. In the dialog that opens, review the External Actors and Pivot Type settings. External Actors lets you use the One File per Actor (OFPA) system. Pivot Type offers Center Min Z, Center, or Pivot Actor. If you select Pivot Actor, choose the Actor to use from the dropdown list.

4. Confirm your selections and save the created Level Instance, or the Level and Packed Level Blueprint.

When a Level Instance is created, a new Level Instance Actor takes the place of the selected Actors in the scene. The source Actors appear as children of this Actor in the Outliner and cannot be selected individually. Transforms applied to the Level Instance Actor are applied to the level it represents. Creating a Packed Level Blueprint instead creates a Packed Level Actor in the scene, linked to the associated Packed Level Blueprint.

Editing instances and committing changes

To edit a Level Instance in the context of the scene, select it in the Viewport, right-click, and choose Level › Edit. Alternatively, click the Edit button in the Details panel. During editing, other Actors in the world appear faded, bringing the contents of the instance you are working on into focus.

When you are finished, select the Level Instance Actor in the Outliner and click Commit Changes in the Details panel. Committing the changes propagates them to other copies of the same Level Instance. To exit editing without saving the changes, press Esc twice.

Packed Level Blueprint editing uses a different interface. Find the instance in the Outliner and use the Edit button, or open the Blueprint in the Content Browser; either action opens the Blueprint Editor window. Edits made here are also reflected in other copies.

The Break operation removes the Level Instance Actor or Packed Level Actor from the world and restores the original assets used to create it. However, the operation cannot be undone. It also does not delete the Level Instance or Packed Level Blueprint from the Content Browser. Use Break only when you intend to convert the structure in the scene back to its original assets.

World Partition: runtime streaming and architectural scenes

Runtime streaming for Level Instances and Packed Level Actors depends on World Partition settings. According to the documentation, the streaming mode is set to Embedded Mode or Level Streaming Mode, and these mode settings cannot be edited. So, these modes should not be treated as simple settings that users can select and change.

Embedded Mode is the default runtime mode and is recommended as the method for streaming level content. Actors inside Level Instances that use OFPA are added to the World Partition grid at runtime; in this workflow, Level Instances exist within the editor. However, some Actors that do not use OFPA may disappear at runtime in Embedded Mode. The documentation gives AWorldSettings as an example of this behavior.

Level Instances that do not use OFPA cannot be embedded in the World Partition grid; at runtime, they load the associated level using Level Streaming Mode. This behavior occurs when the Level Instance Actor is loaded through its own World Partition runtime cell. According to the documentation, this method adds more levels to the streaming process, creating additional runtime overhead, and is not recommended for high-density use because of its performance impact.

In projects using World Partition, Level Instances and Packed Level Blueprints support Data Layers. Actors inside them inherit the Data Layer assigned to the Level Instance Actor by default; additional Data Layers can also be assigned to those Actors. For example, a Level Instance containing house assets can be assigned to a neighborhood layer, while its holiday-themed items can be kept in separate layers that are visible only when the relevant holiday Data Layer is enabled.

For architects, interior designers, and visualization teams, the choice depends on whether the repeating group is an editable collection of Actors or a dense structure made up of static meshes. Level Instance may be suitable for the former, and Packed Level Blueprint for the latter. In World Partition projects, test OFPA usage and the runtime behavior of Actors that do not use OFPA. The source documentation does not specify hardware or licensing requirements; nor does it quantify the rendering optimization offered by Packed Level Blueprint as a specific performance gain.

Common mistakes

• Treating Level Instance and Packed Level Blueprint as the same structure: the former groups Actors in a sublevel; the latter combines static meshes in a Blueprint Actor.

• Skipping Commit Changes after making edits: commit Level Instance changes so they propagate to other copies.

• Assuming World Partition modes can be freely changed: according to the documentation, the modes are determined by World Partition settings and cannot be edited.

• Treating Break as reversible: the operation cannot be undone, so first consider its effect on the scene and the conversion you need.

• Overlooking the runtime behavior of instances that do not use OFPA in Embedded Mode: some Actors, including AWorldSettings, may not be available at runtime.