In a large bowl, mix yogurt, cream cheese, granulated sugar, and vanilla together.
Fold in grapes.
Sprinkle brown sugar and pecans on top.
Serve immediately, or cover and chill until ready to use.
Notes
Grapes: Feel free to use red or green grapes or a combination of the two.
Greek yogurt: You can use 0%, 2% or full-fat Greek yogurt. Sour cream (full-fat or lite) can also be used. I don't recommend using fat-free sour cream.
Cream cheese: Full-fat, reduced-fat, or Greek yogurt-style cream cheese will work. I don't recommend using fat-free.