Converting dessert recipe to gluten free

I am going to make this family favorite recipe using King Arthur gluten free flour. Do you recommend I add 1-2 tsp.xanthan gum?
everything else per recipe.

Marionberry Crunch Bars
From Marsee Bakery

Makes 24 bars

Crust:
¾ cup (1 ½ stick) unsalted butter, room temp and cut into chunks
3/4 cup powdered sugar
2 cups all purpose flour
¼ tsp salt

Filling:
½ c granulated sugar
1 tablespoon corn starch (use 2 tablespoons if the berries are real juicy or using frozen berries)
Pinch of salt
4 cups marionberries
1 ½ tsp grated or minced lemon zest

Topping:
½ c butter, room temp and cut into chunks
1 cup granulated sugar
½ tsp ground cinnamon
¼ tsp salt
1 cup all purpose flour
¼ tsp vanilla
Preheat oven to 350. Lightly grease a 9 x 13 glass baking dish. Set aside.
Crust: Using the paddle attachment of mixer mix butter, sugar, flour and salt; low speed.
Press the mix evenly into bottom of prepared baking dish. Bake until surface is dry and edges are lightly browned; 20 – 25 min. Let cool completely.
Filling: In a mixing bowl combine the sugar and cornstarch and salt. Stir in the berries and lemon zest until well blended. Set aside
Topping: With the paddle attachment of the mixer mix butter, sugar, cinnamon, salt flour, and vanilla; low speed. Until the butter is small pea-size chunks and the mix begins to clump together.
Assemble: Spread the filling on the cool crust; spread the topping over the filling. Bake until topping has browned slightly and the filling bubbly; approx. 40 min. Cool on a rack before cutting into bars.