[danudey]

It also won't satisfy the definition of free/open source software in that the source code likely won't be available under an open-source license (though they're using GitHub, so maybe).

They didn't say word one about the code being open; just the development process and the progress they're making.

[eyko]

> All code and content will be available live to UE4 developers on GitHub.

[krisdol]

On a private repository with a non-OSS-Compatible EULA