As shown on the Social Security Administration website, Medicare Part B is changing in 2023. The chart below details when Medicare Part B becomes effective in 2023:

Once your client is eligible at age 65, their Initial Enrollment Period (IEP) begins 3 months before their 65th birthday, includes the month they turn age 65, and ends 3 months after that birthday.
If they accept the automatic enrollment in Medicare Part B or if they sign up during the first 3 months of their IEP, their coverage will start the month they’re first eligible. If they sign up during the month they turn 65 or during the last 3 months of their IEP, their coverage starts the 1st day of the month after you sign up.