You likely lose that price in December. I got an email telling me so and I believe it applies to all of us grandfathered in. Here’s the relevant part of the email:
As a long-standing and valued member, you are currently paying a lower rate for Premium than the rate available to new subscribers. To show our appreciation for your loyalty, we’re giving you at least three extra months at your current price before the price increase will impact your plan. Your price will not increase before your December billing date. Don’t worry, we’ll be sure to notify you again at least 30 days before the new price is effective.