A transition fill or 30-day temporary non-formulary drug supply is available to:

• People who did not change their Medicare plan coverage from the previous year and now find that their medications are not covered due to annual formulary changes.  For example, you were in drug plan ABC in 2023 and in 2024 you now find that Medicare Part D plan ABC no longer covers your medications that you used last year.
  
  
• People who have joined a new Medicare prescription drug plan during the annual Open Enrollment Period (AEP) that runs from October 15th through December 7th each year.  For example, you were in 2023 Medicare Part D plan ABC and during the AEP you joined 2024 Medicare Part D plan XYZ and find that your 2023 prescriptions are not covered by your new 2024 plan XYZ.
  
  
• People who are newly eligible Medicare beneficiaries and previous had other healthcare coverage.
  
  
• People who have changed Medicare plans during the year.

According to the Centers for Medicare and Medicaid Services (CMS):

"A Part D sponsor’s [Medicare Part D plan or Medicare Advantage plan that includes prescription drug coverage] transition process is necessary with respect to the transition of:

(1) new enrollees into prescription drug plans following the annual coordinated election period [or AEP];

(2) newly eligible Medicare beneficiaries from other coverage;

(3) enrollees who switch from one [Medicare Part D] plan to another after the start of the contract year;

(4) current enrollees affected by negative formulary changes (as defined in section 30.3.3.1) across contract years; and

(5) enrollees residing in LTC facilities (see section 30.4.6 [Emergency Supply for Current Enrollees])."

Remember, CMS defines the purpose of a transition fill as:

"[P]roviding a transition supply is to promote continuity of care and avoid interruptions in drug therapy while a switch to a therapeutically equivalent drug or the completion of an exception request to maintain coverage of an existing drug based on medical necessity reasons can be effectuated."

Sources:

CMS Medicare Prescription Drug Benefit Manual, Chapter 6 – Part D Drugs and Formulary Requirements, Section 30.4 - Transition (Rev. 18, Issued: 01-15-16, Effective: 01-15-16; Implementation: 01-15-16)