The opt-in deadline for the Blended Retirement System is December 31, 2018. Make your decision knowing only you can determine which system is best for you, and understand that if you opt into BRS, it is irrevocable. You only have one chance to make this choice, so it’s imperative you and those involved in making financial decisions for your family fully understand the pros and cons of both retirement systems.

https://www.af.mil/News/Article-Display/Article/1704367/chief-wright-to-airmen-know-your-retirement-options/ Chief Master Sgt. of the Air Force Kaleth O. Wright