42 C.F.R. § 412.533
(a) Duration of transition periods. Except for a long-term care hospital that makes an election under paragraph (c) of this section or for a long-term care hospital that is defined as new under § 412.23(e)(4), for cost reporting periods beginning on or after October 1, 2002, and before October 1, 2006, a long-term care hospital receives a payment comprised of a blend of the adjusted Federal prospective payment as determined under § 412.523, and the payment determined under the cost-based reimbursement rules under Part 413 of this subchapter.
(c) Election not to be paid under the transition period methodology. A long-term care hospital may elect to be paid based on 100 percent of the Federal prospective rate at the start of any of its cost reporting periods during the 5-year transition periods specified in paragraph (a) of this section. Once a long-term care hospital elects to be paid based on 100 percent of the Federal prospective payment rate, it may not revert to the transition blend.
(2) Notification requirement to make election.