Google Drive has a new annual billing option for 100GB and up, so if you're on one of those plans and would rather set yourself up for the entire year as opposed to shelling out for the drive storage on a monthly basis, then you'll now have the opportunity to do so. The benefit of annual billing, of course, is saving money. While you have a higher up front cost then you would if you simply paid for one month, you'll end up saving a little bit over the course of the year which is typical with most services that offer this type of payment option for customers.
If you pay for additional Google Drive storage, you can choose to pay annually with the 100GB plan and the 1TB plan, which equals out to $19.99 a year for 100GB, or $99.99 a year for the 1TB of storage. This is in comparison to either $1.99 a month or $9.99 a month, and it works out to where customers can save 16% each year on the cost of the 100GB plan, or 17% each year on the cost of the 1TB plan. At the moment this only seems to be an option for personal accounts as there is no option for Google Apps Accounts to pay for the service annually. Having said that, the option should be coming, there is just no detail as to when Google will set it up.
To switch to annual billing, the process is pretty simple and you can switch to paying from monthly to annual either from the desktop or from the mobile app. On desktop, simply open up Drive and head to the settings option, and in there you should see the ability to manage your plan. Head to the same place within the Google Drive app, and if you're not sure how to access the settings, you can jump to it from the hamburger menu on the left hand side of the screen. If you're not seeing the option to pay for the extra storage annually then it's likely that the rollout just hasn't happened for everyone yet, or the option to pay annually just isn't available in your region.