src/CI_Base_Model.php
public function get_next_id()
    {
        return (int) $this->_database->select('AUTO_INCREMENT')
            ->from('information_schema.TABLES')
            ->where('TABLE_NAME', $this->_database->dbprefix($this->get_table()))
            ->where('TABLE_SCHEMA', $this->_database->database)->get()->row()->AUTO_INCREMENT;
    }
public function get_next_id()
    {
        return (int) $this->_database->select('AUTO_INCREMENT')
            ->from('information_schema.TABLES')
            ->where('TABLE_NAME', $this->_database->dbprefix($this->get_table()))
            ->where('TABLE_SCHEMA', $this->_database->database)->get()->row()->AUTO_INCREMENT;
    }
Return the next auto increment of the table. Only tested on MySQL.