Long have many of us waited for Google to add an annual billing option to Google Drive, and probably mostly because we hoped it would come with a discount. It appears today is the day: Google Drive now has options for yearly subscriptions, saving you 16-17% versus the current monthly scheme. The annual plans are offered only at the 100GB and 1TB tiers, at $19.99 and $99.99, respectively. The 1TB annual plan brings Google Drive back into line with pricing for Dropbox Pro, Drive's main competitor. Google's support page hasn't even been updated with this info yet, so it looks like we managed to catch this right as Google flipped the switch.
Presumably, if paid Drive subscriptions were available in your country previously, the annual subscriptions should now be live as well. Just head to the Drive storage settings page here to switch over to the annual plans. The plans may still be rolling out, but most of the AP team is seeing them live now.
Note: Annual plans don't appear to be live for Google Apps accounts yet.