Thanks! We write an XML file to Engine/Build/Commit.gitdeps.xml which lists all the binaries you need to have for each commit. The first time you run Setup.bat/Setup.sh, it creates a Git hook to run a program called GitDependencies when you checkout or merge, and that program compares what’s in your workspace to the manifest and downloads any differences from our CDN. The source for GitDependencies is in the repository under Engine/Source/Programs/GitDependencies, if you want to take a look at it!