The 11 month subscription contract is only available to those who have purchased the Dexcom G6 Starter Kit within the last 50 days.
Since the battery on your transmitter continues to run down even when not in use, if you have waited an extended period of time between purchasing your Starter Kit and transferring to the Subscribe & Save plan the battery life of your transmitter may have expired. You will therefore be offered the 12 month plan and receive all the product you need to continue your Dexcom G6 journey.