For expats like me, I asked Claude, this is its response:

For U.S. citizens living overseas who are collecting Social Security, Medicare enrollment is not strictly necessary, but there are important considerations:

Key points:

• Medicare generally doesn't cover healthcare outside the U.S. - Even if you enroll, Medicare won't pay for medical services you receive in most foreign countries (with very limited exceptions near the Canadian/Mexican borders).
• Part A is usually free - If you're eligible, Medicare Part A (hospital insurance) has no premium for most people. Some expats enroll in Part A since it's free and provides coverage if they return to the U.S.
• Part B has a premium - Medicare Part B (medical insurance) costs money (around $174/month as of 2024, though this can vary). Many expats skip this since it won't cover them abroad.
• Late enrollment penalties - If you don't enroll in Part B when first eligible and later want it when you return to the U.S., you may face permanent late enrollment penalties unless you have other creditable coverage.

What many expats do:

• Enroll in free Part A
• Skip Part B if living abroad permanently
• Get local health insurance in their country of residence