CMS has two big arms - the Center for Medicaid and the Center for Medicare. Under the Biden administration the head of "CM," Center for Medicare, is Dr. Meena Seshamani.
See a new op ed by her on the direction of Medicare at Washington Times - here.
See a new interview with her at JAMA - here (podcast), here (text).
CMS org chart here.
For the annual, multi hundred page MEDPAC report to Congress, March 2022, entry point here.