Letter of credit
(C) Letter of credit. Except as otherwise provided in paragraph (d)(6) (ii) or (iii) of this section, the trust instrument must provide that whenever the letter of credit security arrangement is used for the QDOT, the U.S. Trustee must furnish an irrevocable letter of credit issued by a bank as defined in section 581, a United States branch of a foreign bank, or a foreign bank with a confirmation by a bank as defined in section 581. The letter of credit must be for an amount equal to 65 percent of the fair market value of the trust assets (determined without regard to any indebtedness with respect to the assets) as of the date of the decedent's death (or alternate valuation date, if applicable), as finally determined for federal estate tax purposes (and as further adjusted as provided in paragraph (d)(1)(iv) of this section). If, after examination of the estate tax return, the fair market value of the trust assets, as originally reported on the estate tax return, is adjusted (pursuant to a judicial proceeding or otherwise) resulting in a final determination of the value of the assets as reported on the return, the U.S. Trustee has a reasonable period of time (not exceeding 60 days after the conclusion of the proceeding or other action resulting in a final determination of the value of the assets) to adjust the amount of the letter of credit accordingly. But see, paragraph (d)(1)(i)(D) of this section for a special rule in the case of a substantial undervaluation of QDOT assets. Unless an alternate arrangement under paragraph (d)(1)(i) (A), (B), or (C) of this section, or an arrangement prescribed under paragraph (d)(4) of this section, is provided, or the trust is otherwise no longer subject to the requirements of section 2056A pursuant to section 2056A(b)(12), the letter of credit must remain in effect until the trust ceases to function as a QDOT and any tax liability finally determined to be due under section 2056A(b) is paid or is finally determined to be zero.