Let’s start with your medical benefits. As you probably know when you become eligible for Medicare you generally must have both Medicare Part A and Part B to remain TRICARE-eligible. For most people, this happens at age 65. Thus, you’ll have to enroll and pay the required premiums for Part B to be eligible for TRICARE For Life (TFL). This whole transition should be relatively seamless — we haven’t heard a lot of complaints from folks transitioning from TRICARE to TFL.
The big "change" will be that TRICARE will be secondary to Medicare for services covered by Medicare. Unlike your healthcare benefits, you shouldn’t see any change at all with respect to your military retirement. You’ll officially be "double dipping!"