On December 30, 2021, the Internal Revenue Service (IRS) published final regulations for the IBOR transition. This Legal Update provides background on the principle US federal income tax concern with IBOR-related amendments to existing contracts and an overview of previous IRS guidance aimed at addressing the concern. The Update then discusses the types of modifications that can fit within the final regulations, the relief provided for modifications that do fit and a few questions left open by the IRS.