Pursuant to the U.S. Environmental Protection Agency's Significant New Alternatives Policy program, this action proposes to list the refrigerant 2,3,3,3-tetrafluoropropene, also known as HFO-1234yf, as acceptable, subject to use conditions, in the motor vehicle air conditioning end-use for retrofit of heavy-duty pickup trucks and complete heavy-duty vans. This action supplements the Agency's November 10, 2025, proposal with respect to the proposed listings in the motor vehicle air conditioning end-use for retrofit of heavy-duty pickup trucks and heavy-duty vans (both complete and incomplete vans). The EPA is also supplementing that proposal to clarify the intended scope of that proposed rule. The EPA is providing an opportunity for public comment on the additional listing and the clarification. The EPA is not reopening the comment period for any portions of the November 10, 2025, proposal which are not explicitly addressed in this supplemental proposal. Comments on this supplemental proposal must be received on or before 6 May 2026 unless a public hearing is held. POC is Emily Maruyama tele: (202) 564-2809; email: maruyama.emily@epa.gov. (Federal Register 6 April 2026 [Proposed Rule] Pages 17176-17186)