This bill proposes significant amendments to Title XVIII of the Social Security Act, primarily focusing on Medicare's prescription drug inflation rebate program. Its core objectives are to extend the application of these rebates to drugs sold in the commercial market and to adjust the historical baseline used for calculating inflation. For Medicare Part B drugs , the legislation expands the inflation rebate mechanism to include drugs that would be payable under Part B if furnished to a Medicare enrollee, effectively covering commercial sales. It also revises the calculation of billing units, excluding those paid under Medicaid. Crucially, the bill shifts the base year for Part B rebate calculations from July 1, 2021, to July 1, 2016 , and the corresponding January 2021 to January 2016 , meaning inflation will be measured against an earlier price point. These Part B changes are set to take effect for calendar quarters beginning on or after January 1, 2026. Similarly, for Medicare Part D drugs , the bill applies inflation rebates to units used to determine the average manufacturer price, while excluding units covered by Medicaid, Part B rebates, or the 340B program (starting 2026). The base year for Part D rebate calculations is also moved from October 1, 2021, to October 1, 2016 , and January 2021 to January 2016 . These Part D provisions will apply to periods beginning on or after October 1, 2025.