Well... Sort of free. But here's how you get it!
According to delish.com:
Available in stores now, the 16-ounce Brewed Refill Tumbler can be purchased at any Starbucks store for $40. Once you've got it, you can return every single day in January for a free Grande brewed hot coffee or hot tea.
I'm pretty confident I could make $40 worth it over the course of a month. Because CAFFEINE!