Pull the steaks out at least 10-20 minutes before air frying. Preheat air fryer to 420 degrees Fahrenheit for 5 minutes.
Season both sides of the filets generously with kosher salt and black pepper. Place in the air fryer for 8-9 minutes for medium rare, 10-11 min for medium. For medium well, cook 13-14 minutes. Be sure to flip steaks halfway through the cooking time. Check the internal temperature with a meat thermometer, which should read 140F for medium, 150F for medium-well, and 160F for well done.
Allow the steaks to rest at least 5-10 minutes before cutting into them. Slice a piece of the compound butter and place on the warm steaks.
Garlic Compound Butter
Make the chive butter by combining the garlic, chives, rosemary, a pinch of kosher salt and freshly grated black pepper with softened butter. Stir till fully combined. Place on a piece of saran wrap and roll together to create a small log that's about 1 1/2 inches-2 inches wide. Place in the fridge or freezer.
Notes
Filets used in testing were 1 3/4 inches thick. If yours are thinner, you may need to cut down the cooking time 1-2 minutes.
Don't skip pre-heating the air fryer as this will help the steaks brown on the outside. Also flip halfway through.