Slim is abounding Slim 3?

Slim 4 stable version released not a long ago and many of us going for it but What if I stick to version 3??
Slim 3 Skeleton is not available
Many Slim 3 middlewares are updated for Slim 4 which means the update will not work in older version.

Why not keep them alive for version 3 and create new branch for version 4?

You can still use Slim version 3:
composer require slim/slim "^3.0"

And you can still find and install the Slim 3 Skeleton like this:
composer create-project slim/slim-skeleton=3.1.8 slim3skeleton

I’d say you still have a good year with slim 3 but I dont think any new features will be created for it. Maybe security patches but thats it…