Xpack Alerting is free or must we buy it?

Elastic Stack Elasticsearch
1

hi
im used xpack and xpack alerting
spack is free or purchase ?

2

Alerting is part of the paid level in X-Pack.

3

I din't notice
Should I buy xpack so I can use alerting?

4

Yes. The details are available here: https://www.elastic.co/subscriptions