These expansions are in addition to the complimentary 15GB of Drive space available to all Google users, bringing the allotted storage totals to 65GB and 40GB for the One Max and One, respectively. There are a few caveats, though. According to Mountain View, the HTC One Developer Edition isn't eligible for this due to its unlocked bootloader.
Furthermore, you can only activate this promo once per Google account, which rules out gaming the offer to get even more space. Got all that? Good -- there's a quiz later.