.UCAS File Extension
Unreal Compressed Asset File
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What is a UCAS file?
A UCAS file is a container used by Unreal Engine to store cooked game assets in a compressed, runtime-ready form. It stores binary asset data, such as textures, models, audio, and other bulk data, that the engine loads during gameplay. UCAS files pair with a table-of-contents file (often a .UTOC or .TOC file) that directs the engine to the location of each asset stored inside the container.
More Information
Unreal Engine began using UCAS/UTOC containers as part of newer IO Store and Zen Loader packaging methods (used in recent UE4/UE5 workflows) to improve load performance and reduce runtime overhead. Game developers produce UCAS files when they "cook" and package a project for distribution; the engine then reads UCAS containers at runtime rather than loading many separate files. Because UCAS holds cooked (engine-ready) data, it is not a source or editable asset format, it is a delivery format meant for the running game.
How to open a UCAS file
UCAS files are not meant to be opened. Instead, games built with the Unreal Engine load the files during gameplay.
However, you can open or extract files from a UCAS container with Unreal Engine tools or community utilities that support the IO Store format. The official UnrealPak/IOStore tools included with the engine can list and extract packaged content when present in your engine installation.
To do this:
- Navigate to your Unreal Engine installation folder: Engine/Binaries/Win64/
- Make sure you have the UCAS file and UTOC file, open a command prompt, and run: UnrealEditor-Cmd.exe IoStore -List -Container="path\to\file.ucas" -TOC="path\to\file.utoc"
- Extract the contents by running the following command: UnrealEditor-Cmd.exe IoStore -Extract -Container="path\to\file.ucas" -TOC="path\to\file.utoc" -Output="path\to\output_folder" This extracts .uasset, .uexp, .ubulk, and other files to the output folder.
Community tools, such as Archengius ZenTools, also read and convert UCAS/UTOC containers for modding or analysis, but results vary by engine version and game (some UCAS files are serialized specifically for a particular engine build).