Preheat oven to 400°. Place grape clusters on a 15- x 10-inch jelly-roll pan. Stir together cranberries, olive oil, and rosemary in a small bowl. Spoon mixture over grape clusters.

Bake at 400° for 15 to 18 minutes or until grapes begin to blister and cranberries start to pop, shaking pan occasionally. Serve immediately, or let stand up to 4 hours.