Is Metribeat modules beat-xpack, elasticsearch-xpack and logstash-xpack are free or paid?

Is monitoring beats, Elasticsearch, logstash and kibana with Metricbeat using x-pack modules is free or licence ?
Simply Monitoring ELK stack with Metricbeat is free or require licence?

Licensing details are described here: https://www.elastic.co/what-is/open-x-pack

Thank you Mtojek.