If you are using a tough cut of meat let it marinate for 10-15 minutes. Sirloin, ribeye or NY strip shouldn't need to marinate.
Preheat the air fryer at 400 F for 3 minutes. Then add the steak cubes to the air fryer basket. Don't overcrowd the basket and cook in batches if you need to.
Total cooking time will depend on your desired degree of doneness. Here are approximate total cooking times.medium-rare: 7 minutesmedium: 8 minutesmedium-well: 10 minuteswell-done: 12 minutes
Air fry at 400 F for 5 minutes. Then pull the basket out and flip the pieces over.
Air fry for the remaining time for your desired degree of doneness, which will be 2-7 minutes more.
Check the internal temperature of a few of the larger pieces.
To make the optional herb butter:
Mix the softened butter with the fresh thyme.
1 tablespoons butter
Add the herb butter to the cooked steak bites and stir so that it melts and coats them.
1/2 tablespoon fresh thyme
Notes
You can substitute garlic butter or another type of herb butter. Or skip the butter completely.
Cut the meat into similar size pieces so it cooks evenly.
Let the meat marinate for 10-15 minutes (or longer) if using a tough cut of beef.
Use a thermometer to check the internal temperature to ensure they are cooked to the doneness you prefer.