According to a paper produced by the Kaiser Family Foundation, the $8000 you reference as a cap in 2024 is not simply out of your pocket but a combination of out of pocket AND something related to the drug manufacturer.

Here is the exact quote:

"In 2024, the catastrophic threshold will be set at $8,000. This amount includes what Part D enrollees spend out of pocket plus the value of the manufacturer price discount on brands in the coverage gap phase. At this amount, Part D enrollees who take only brand-name drugs in 2024 will have spent about $3,300 out of their own pockets and will then face no additional costs for their medications."

The entire Kaiser issue paper can be accessed here. https://www.kff.org/medicare/issue-brief/changes-to-medicare-part-d-in-2024-and-2025-under-the-inflation-reduction-act-and-how-enrollees-will-benefit/

I do not pretend to understand this but if I was looking at needing to have very pricey meds, I would study this 2024 change very carefully and try to get a complete understanding.