In a small bowl, combine the warm water, sugar, and yeast. Stir gently and let sit for 8 to 10 minutes until bubbly and foamy.
In a large bowl, whisk together the gluten free flour, tapioca starch, psyllium husk powder, and salt.
Add the egg whites, olive oil, and apple cider vinegar to the yeast mixture. Whisk to combine, then pour into the dry ingredients. Stir vigorously for about 3 minutes until a very wet, sticky batter-like dough forms. This dough is meant to be very loose and wet, which is what creates ciabatta's signature open crumb.
Cover the bowl tightly with plastic wrap and let the dough rise in a warm spot for about 60 to 75 minutes, until it has roughly doubled in size and looks bubbly throughout.
Line a baking sheet with parchment paper and generously dust it with gluten free flour. Gently scrape the dough onto the prepared sheet without deflating it too much. Using well-floured hands, gently shape it into a rough rectangle about 10 by 6 inches. The shape should be rustic and imperfect.
Dust the top lightly with gluten free flour. Let it rest uncovered for 20 minutes while you preheat the oven. Preheat the oven to 425 F. Place an oven-safe dish on the bottom rack. Pour half a cup of hot water into the dish right before placing the bread in the oven to create steam.
Bake for 24 to 30 minutes, until the crust is golden and crisp and the loaf sounds hollow when tapped on the bottom. Let it cool on a wire rack for at least 20 minutes before slicing.