If you own an HTC One or an HTC One mini, or if you plan to purchase the HTC One max, Google and HTC have a great deal for you. You get 50GB of extra, free cloud based storage for two years on Google Drive with an HTC One max. Meanwhile the HTC One or the HTC One mini will get you 25GB of Google Drive storage for two years.In order to get the offer you will have to get the Android 4.3 update with Sense 5.5 first. No device with an unlocked bootloader will be included in the offer with means that the HTC One Developer Edition is not eligible for the storage.
Once your HTC One or HTC One mini is updated to Sense 5.5 (which comes out of the box on the HTC One max), you can access your free storage. To redeem the offer, open the Google Drive app. Press "Redeem" and then follow the screen prompts. Google suggests that you have a Wi-Fi connection when redeeming the storage offer, which is good until January 1st, 2016. Once your two-years is up, your data remains available in Google Drive for you to access, download, or share.There are some rules through. In order to redeem the free offer one time for each device. Using the same Google account you can redeem one +50GB offer and one +25GB offer on two eligible devices. If you need more storage, it can be purchased from Google. Also keep in mind that Google offers 15GB of free storage with Google Drive right off the bat, which includes your Gmail account.
source - Google | Android Police