It's known as Exodus SDK, and has a bunch of integrated features.
4A Games has announced that Metro Exodus now has a fully integrated mod editor. Known as Exodus SDK, this feature allows players to create standalone content from an editor suite that is "as it was the day we released Metro Exodus".
It's noted in a recent blog post that the Editor SDK suite has full Mod.io support, as well as the ability to easily share your produced content, all on top of a visual script editor, tutorial levels, and a fully unpacked sandbox level.
4A Games has noted that there is a slight caveat in what you can do with the editor suite, including that it cannot be used for commercial purposes, meaning it is solely designed to produce free additional community-made content.
The developer has also affirmed that it will not be getting into the engine licensing business, and that this is simply "something meant for the community".
While you can check it out today, the Exodus SDK engine will be continuously improved on a daily basis.