Allow tenderloin to come to room temperature. (About 30 minutes).
Preheat Air fryer to 400°.
Pat tenderloin dry and rub the tenderloin all over with olive oil. Season all sides with fresh ground sea salt and fresh ground black pepper. See Note 1 for variations.
For medium rare cook 22 minutes flipping at midpoint of cooking. You want to remove the tenderloin from the Air Fryer when it is about 5° below your final target temperature. Check internal temperature and adjust timing by just a couple of minutes at a time. See the chart below for suggested timing for different degrees of doneness. These times will also vary with the size of your tenderloin and the power of your air fryer.
Internal temperature of 125° for blue -check temperature at about 18 minutes;Internal temperature of 135° for rare - check at about 20 minutes;Internal temperature of 145° for medium rare- check at about 22 minutes;Internal temperature of 150° for medium well, check at about 24 minutesInternal temperature of 160° for well done- check at about 27 minutes. Remove from oven at 5° below final desired temperature. Cover and allow tenderloin to rest for 5 minutes.
Slice and serve with desired sauce or condiments.
Notes
Note 1: If not planning to serve with a sauce you may choose to include ½ teaspoon of garlic and/or onion powder in the rub.