I was using the devkit setup while Kirby was in beta, because I very much like the approach of having a public folder and keeping most of the stuff outside of it.
As soon as I update Kirby from the latest beta to 3.0.0, a new folder /kirby/vendor/ appears which seem to be a duplicate of /vendor.
I’m pretty sure that I can ignore this new folder, does anyone know what’s the correct setup keep using the devkit with 3.0.0?
You can safely ignore the /kirby/vendor folder. If you take a look in the /kirby/bootstrap.php file you will see that it checks if there’s a /vendor folder on the root and loads it instead of the /kirby/vendor one.
Yep. We added that directory to make it possible to install Kirby as a Git submodule without having to jump through too many hoops. If Kirby is installed via Composer, that directory does nothing whatsoever. 
You can actually ignore the whole kirby folder as it will be installed by Composer anyway.
Thanks for the replies.
Are you sure, @lukasbestle? I thought the composer-installer automatically moves the content of /vendor/getkirby/cms to /kirby!?
That’s exactly right. And because it does, you can ignore /kirby. If it doesn’t exist, Composer will create it when you run composer install.