Just got this email from Strava, sweet! I've almost pulled the trigger on renewing my Zwift for the winter, glad I waited.
Starting in 2017, your Premium membership will no longer include two free months of Zwift. Until then, we want you to squeeze every drop out of this benefit. That's why Zwift will be offering every Premium cyclist free access all November and December - whether you've used your free two months this year or not.
Hope you enjoy it. We'll see you out there on the (virtual) road.
The Strava Premium Team
And here's the details on the Zwift site: