In Drupal 7 and earlier, system configuration and state were commingled in the variables table. In addition to the new Configuration API, Drupal 8 added the State API. This should be used for settings that are:

• Specific to an individual environment and should not be deployed between environments
• Can be reset without adverse consequences

This encompasses items such as the last cron run timestamp, CSRF tokens, and so on. Typical uses include:

• Getting a state variable:

      $val = \Drupal::state()->get('key'); 

• Setting a state variable:

      \Drupal::state()->set('key', 'value'); 

• Deleting a state variable:

      \Drupal::state()->delete('key');