Include model inside a model

Hello! We are finally ready to use CodeIgniter 4. I only have some problems with using a model inside a model. I was expecting that I could use something like this:

PHP Code:

namespace App\Models;
use CodeIgniter\Model;
class Filters_model extends Model {

    function __construct(){
        // Call the Model constructor
        parent::__construct();
        $this->session = session();
        $this->customers = model('Customers_model');
    }
} 


But that doesn't seems to work. I'm getting a "Service Temporarily Unavailable" error. In CI3 you could just put it in autoload and use it wherever you like.

How can I include a model inside a current model to use those functions of that model?