Exemple: $site_name = \Drupal::config('system.site')->get('name');
// Set the site name.
\Drupal::configFactory()->getEditable('system.site')->set('name', 'My site')->save();
Today we released Drupal 8.0.0, the first fully supported release of Drupal 8! This is the biggest update ever to Drupal, our open source content management platform. Here are just a few of the hundreds of improvements in Drupal 8: