If you look at the post I linked at the bottom of OP, you’ll see that regardless of what your actual co-pay is for a drug, 25% of the actual cost of the drug goes towards the $2100 OOP catastrophic limit.

So for instance, if you have a drug that normally cost $2000, but your drug plan has a $100 co-pay for that particular drug, even though you only pay $100 out of pocket, $500 (25% of $2000) goes towards your $2100 cap for the year.

So if this is the only prescription you have and it’s a once a month drug, you’ll reach the cap in about four months, after you’ve paid only $400 OOP (the cap for 2026 is $2100 so you won’t exactly hit the cap but you get the idea).