Wash grapes and remove stems. Dry completely.
In a large bowl, beat cream cheese with a handheld mixer until completely smooth. Add sour cream, sugar, and vanilla. Mix for 2 minutes on medium speed.
Add grapes to cream cheese mixture and gently mix by hand until all grapes are covered. Cover and chill until ready to serve.
Just before serving, sprinkle pecans and brown sugar on top of grape salad.