26 C.F.R. § 1.72-12
If a contract to which section 72 applies provides for the payment of a lump sum in full discharge of the obligation thereunder and the obligee entitled thereto, prior to receiving any portion of such lump sum and within 60 days after the date on which such lump sum first becomes payable, exercises an option or irrevocably agrees with the obligor to take, in lieu thereof, payments which will constitute "amounts received as an annuity", as that term is defined in paragraph (b) of § 1.72-2 , no part of such lump sum shall be deemed to have been received by the obligee at the time he was first entitled thereto merely because he would have been entitled to such amount had he not exercised the option or made such an agreement with the obligor.
26 C.F.R. §1.72-12