For purposes of this subtitle, if both the executor (if any) of an estate and the trustee of a qualified revocable trust elect the treatment provided in this section, such trust shall be treated and taxed as part of such estate (and not as a separate trust) for all taxable years of the estate ending after the date of the decedent’s death and before the applicable date.
26 U.S. Code § 645 - Certain revocable trusts treated as part of estate
(a) General rule
(b) DefinitionsFor purposes of subsection (a)—
(1) Qualified revocable trust
(2) Applicable dateThe term “applicable date” means—
“The amendments made by this section [enacting this section and amending section 2652 of this title] shall apply with respect to estates of decedents dying after the date of the enactment of this Act [Aug. 5, 1997].”