Place the steak in a large mixing bowl. Top with the soy sauce, brown sugar, garlic powder, and black pepper. Stir to combine, making sure all the cubes are evenly coated.

Let the steak marinade at room temperature for 20 to 30 minutes (you can skip this step if you're short on time, but marinating does result in more flavorful meat).

When ready to cook, preheat your air fryer to 400°F. Arrange the steak bites in the air fryer basket in an even layer. Don’t overcrowd the basket and cook in batches if needed—the steak bites shouldn't touch.

Air fry steak bites at 400°F for 4 to 6 minutes, depending upon how well done you like your meat, shaking the basket halfway through (I remove mine at 135°F for medium—note the steak bites' temperature will rise as they rest).

Remove the steak bites to a plate and let rest for at least 5 minutes. Repeat with remaining batches.