The source for the installer is under Engine/Source/Programs/PrereqInstaller. If you use Perforce to get the Unreal Engine source code, you'll also find precompiled binaries in the same Engine/Extras/Redist/en-us folder of the Perforce repository. You can find the installer, with separate executables for 32-bit and 64-bit Windows, in the Engine/Extras/Redist/en-us folder under your Unreal Engine installation location. However, you may need to run the prerequisite installer yourself if you build Unreal Engine from source, or if you need to prepare a computer with all the Unreal Engine prerequisites for a specific purpose-for example, if you are setting up a fresh computer to act as a Swarm Agent.

When you install Unreal Engine through the Epic Games Launcher, the Launcher automatically installs these prerequisites for you. The Unreal Engine includes a prerequisite installer that installs everything needed to run the editor and engine, including several DirectX components and Visual C++ redistributables. Software Installed by the Prerequisite Installer

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