@Leo47 is correct about gold members. I used it the all the time. Basically, you get a basic tea or coffee, in the am. Then, a refill when you go lunch.
From Starbucks members page:
do free refills work?
Published 09/04/2012 01:22 PM | Updated 08/11/2017 11:01 PM
When you use your registered Starbucks Card or Mobile app to purchase any handcrafted beverage and then present that same Starbucks Card or Mobile app, you can get
free refills of brewed coffee (hot, Iced Coffee or Cold Brew), and tea (hot, or iced) during the same store visit regardless of the original beverage at participating Starbucks stores.
Once you leave the store, your visit has ended and any subsequent coffee or tea
refill thereafter would be considered a new purchase.
Refills are not available in the Drive Thru.