Rinse all four russet potatoes under cold running water and scrub away any dirt from the skin. Pat each potato completely dry with paper towels — no surface moisture should remain, as it will prevent the skin from crisping.
Using a fork or thin skewer, pierce each potato approximately 10 to 12 times all around, spacing holes about 1 inch (2.5 cm) apart and at least 1/2 inch (1.25 cm) deep. This step is essential to allow steam to escape during cooking.
In a mixing bowl, stir together the olive oil, kosher salt, garlic powder, and black pepper. Coat each potato thoroughly on all sides with the seasoned oil mixture using your hands or a pastry brush.
Set your air fryer to 400°F (200°C) and allow it to preheat for 3 to 5 minutes. Preheating ensures the potatoes start crisping immediately when they go in.
Place the seasoned potatoes directly in the air fryer basket without foil, leaving at least 1/2 inch (1.25 cm) of space between each potato so hot air circulates freely. Cook in batches if needed.
Air fry at 400°F (200°C) for 20 minutes, then use tongs to flip each potato and cook for another 15 to 20 minutes, until the total cook time reaches 38 to 45 minutes for large potatoes.
Insert an instant-read thermometer into the center — it should read 210°F (99°C). Alternatively, pierce with a fork; if it slides in with no resistance, the potato is done. Add 5 more minutes if needed.
Let the potatoes rest 2 to 3 minutes, then cut a deep X into the top of each and push the ends inward to open. Add butter and any desired toppings and serve immediately.