Decaffeinated, not caffeine-free
Starbucks lists 15 mg of caffeine for a Short Decaf Pike Place Roast, 20 mg for a Tall, 25 mg for a Grande, and 30 mg for a Venti. That is a small fraction of regular Pike Place Roast, which carries 315 to 390 mg in a Grande, but it is not zero. Decaffeination removes most of coffee’s caffeine, not all of it, which matches the FDA’s general note that decaffeinated coffees and teas “still contain some caffeine.”
For general background on decaf across brands, see caffeine in decaf coffee, which covers USDA’s home-brewed figures alongside Starbucks’ own.
Where those 25 mg land
A Grande decaf carries about as much caffeine as a Grande Caffè Misto has in roughly a sixth of its dose, and less than a Grande Starbucks hot chocolate. For most healthy adults working to the FDA’s 400 mg daily figure, twelve Venti decafs would fit in a single day; this is not a drink that meaningfully counts against a normal limit.
When it still matters
Three situations make the small number worth tracking. In pregnancy, where ACOG uses a 200 mg daily ceiling, decaf is one of the easiest swaps to make, though several large decafs a day are not literally zero. Anyone told to avoid caffeine completely, for a medical reason or a sensitivity, should know that decaf is a reduction, not an elimination. And late at night, even 25 to 30 mg adds a little to whatever earlier coffee is still circulating, given caffeine’s mean half-life of about five hours (NCBI).