Project Fi today added a new data usage tracking feature. Users will be able to see specific data usages broken out by application.
Users will need to be on Android Nougat, and have at least version K.2.7.20 or later of the Project Fi app. In addition, to the current data usage breakdown, there will also be access to see the breakdown of usage for recent statements as well.
It seems to me that this will just be pulling the information from the data usage table on the device. Here you can see current usage as well as select a recent billing cycle from in the device settings. You can only see the data usage for the current device you are on, so it does seem that it is remaining local and just pulling the data from the device data settings screen.
It should be noted that if you are in a group plan, currently you cannot see the app data usage of group members.
Not sure this is a necessary feature since the device already has it, but let us know your thoughts in the comments.