This bill amends the Social Security Act to impose new requirements on Medicare Part D prescription drug plans (PDPs) and Medicare Advantage (MA-PD) plans regarding their formularies. These changes, effective January 1, 2028, aim to increase access to and affordability of generic drugs and biosimilar biological products for Medicare beneficiaries. The legislation mandates their inclusion on formularies and establishes specific cost-sharing rules to reduce out-of-pocket expenses. Specifically, if a plan's formulary includes a part D reference drug , it must also include all corresponding part D generic drugs with a lower wholesale acquisition cost. Similarly, if a formulary lists a part D reference biological product , it must include at least one available part D biosimilar biological product with a lower wholesale acquisition cost. Plans are prohibited from imposing more restrictive access limits, such as prior authorization or step therapy, on these required generic and biosimilar options compared to their brand-name counterparts. Furthermore, the bill introduces new cost-sharing tiering requirements for plans utilizing tiered cost-sharing. Such plans must establish at least one tier exclusively for part D generic drugs and part D biosimilar biological products . For this dedicated tier, the cost-sharing must be either zero or a copayment at least $20 lower than that of the lowest branded drug tier. If a plan includes a specialty tier, it must create a second specialty tier specifically for high-cost part D generic drugs and part D biosimilar biological products , provided their reference products are on higher cost-sharing tiers or excluded. This second specialty tier must feature a coinsurance rate at least 5 percentage points lower than other specialty tiers. The legislation also restricts deductibles from applying solely to generic or biosimilar drugs unless they apply broadly to other covered Part D drugs.