I'm using now splunk Enterprise 7.0.1. Right now I'm quite new to it that's why i'm asking. Is there a way to get data(logs etc.) from Google Cloud Platform with this version ? Or I have to get version 6.5 and install the add ? I'll be really grateful for every answer.
One potential option for you would be to install Splunk Enterprise 6.5 on a second box, and set it up to act as a heavy forwarder. This being, a full Splunk Enterprise instance, whose purpose is to pull in data, such as by the GCP add-on, (and other apps, such as DBConnect), and forward it on to other Splunk instances in your environment.
Otherwise, if you have a distributed deployment (separate instances for search heads and indexers), you could simply point this new heavy forwarder to output data to your indexing tier. In either case, it would allow you to install the add-on on the last known supported version of Splunk Enterprise.