According to this post, Bootstrap 4 offers an opt-in flex box grid.
There’s a boolean variable in the _variables.scss file called $enable-flex. If you set this to true and recompile, a ton of things happen.
Q: How do you recompile Bootstrap? I typed:
git clone https://github.com/twbs/bootstrap
on the command line and my windows computer just hung. I finally had to Ctrl+C and exit.
It looks like scotch.io has a flex box compiled version.