Google Fi is one of the best carriers, especially in the United States, when it comes to international roaming. International data costs the same as domestic rates, cellular calls are $0.20 per minute, and there's even free texting. Google Fi also gives you alerts when you're reaching your data cap. Well, except for international data usage.
But all that is changing, and starting now you will receive alerts for international data usage like you would domestically. This is the first phase of improvements to Google Fi's international tracking, according to Reddit user /u/ProjectFiCM (who has been verified to actually be from Google). Phase two, for which a date has not been formally announced, includes adding international data usage to Google Fi's in-app data usage graph.
As with almost everything Google announces, this is being gradually rolled out to users, so you may not see a change right away.