Getting Started with CodeIgniter 4 PreAlpha 1

So migration will be impossible without rewriting your app.

Ya sure. Rewrite means I can not use existing code in any situation?
I understand I have to change the code where I created and called model.

for example
$this->load->model('user');

to
use App\Models\User; and than dependency injection.

Or I have to start from scratch??

Edit.
I want to use CI4 but its not ready yet. And I can't wait for it.