The out-of-pocket maximum is a cap on what you'll pay for covered care in a plan year — including deductibles, copays, and coinsurance. Once you hit this limit, your insurance covers 100% of additional covered costs, including ongoing GLP-1 prescriptions, for the rest of the plan year.
HealthCare.gov's definition adds that the 100% applies to covered in-network care (HealthCare.gov (external link)).