You incur commitment once you begin your junior year OR you activate a scholarship. This is called "contracting."

Upon graduation, you will be commissioned as a Second Lieutenant in the active duty Air Force. Your commitment is 4 years, whether you are on scholarship or not. Pilots, navigators, doctors and lawyers have an extended commitment. Pilots serve a minimum of 10 years, navigators serve 8 years and Air Battle Managers serve a 6-year commitment. Doctors and lawyers serve the equivalent to their years of education in their field.