<PAGE>

                                                                    Exhibit 4.01

          This Note is a Global Security within the meaning of the Indenture
hereinafter referred to and is registered in the name of the Depository named
below or a nominee of the Depository. This Note is not exchangeable for Notes
registered in the name of a Person other than the Depository or its nominee
except in the limited circumstances described herein and in the Indenture, and
no transfer of this Note (other than a transfer of this Note as a whole by the
Depository to a nominee of the Depository or by a nominee of the Depository to
the Depository or another nominee of the Depository) may be registered except in
the limited circumstances described herein.

          Unless this certificate is presented by an authorized representative
of The Depository Trust Company, a New York corporation (the "Depository"), to
the Company or its agent for registration of transfer, exchange, or payment, and
any certificate issued is registered in the name of Cede & Co. or in such other
name as is requested by an authorized representative of the Depository (and any
payment is made to Cede & Co. or to such other entity as is requested by an
authorized representative of the Depository), ANY TRANSFER, PLEDGE, OR OTHER USE
HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the
registered owner hereof, Cede & Co., has an interest herein.

                                 CITIGROUP INC.
                         5.850% NOTES DUE AUGUST 2, 2016

REGISTERED                                                            REGISTERED

                                                              CUSIP: 172967 DQ 1
                                                              ISIN: US172967DQ13
                                                          Common Code: 026336279

No. R-0001                                                     $________________

          CITIGROUP INC., a Delaware corporation (the "Company", which term
includes any successor Person under the Indenture), for value received, hereby
promises to pay to Cede & Co., or registered assigns, the principal sum of
$_____________ on August 2, 2016 and to pay interest thereon from and including
August 2, 2006 or from the most recent Interest Payment Date to which interest
has been paid or duly provided for, semi-annually, on February 2 and August 2 of
each year, commencing February 2, 2007, at the rate of 5.850% per annum, until
the principal hereof is paid or made available for payment. The interest so
payable, and punctually paid or duly provided for, on any Interest Payment Date
will, as provided in the Indenture, be paid to the Person in whose name this
Note is registered at the close of business on the Record Date for such
interest, which shall be the January 15 and July 15 (whether or not a Business
Day) immediately preceding such Interest Payment Date.

<PAGE>

          Any such interest not so punctually paid or duly provided for will
forthwith cease to be payable to the holder on such Record Date and may either
be paid to the Person in whose name this Note is registered at the close of
business on a subsequent Record Date, such subsequent Record Date to be not less
than five days prior to the date of payment of such defaulted interest, notice
whereof shall be given to holders of Notes of this series not less than 15 days
prior to such subsequent Record Date, or be paid at any time in any other lawful
manner not inconsistent with the requirements of any securities exchange on
which the Notes of this series may be listed, and upon such notice as may be
required by such exchange, all as more fully provided in the Indenture.

          Interest hereon will be calculated on the basis of a 360-day year
comprised of twelve 30-day months.

          If either an Interest Payment Date or the Maturity of the Notes falls
on a day that is not a Business Day, such Interest Payment Date or Maturity will
be the next succeeding Business Day. If a date for payment of interest or
principal on the Notes falls on a day that is not a business day in the place of
payment, such payment will be made on the next succeeding business day in such
place of payment as if made on the date the payment was due. No interest will
accrue on any amounts payable for the period from and after the due date for
payment of such principal or interest.

          For these purposes, "Business Day" means any day which is a day on
which commercial banks settle payments and are open for general business in The
City of New York.

          Payment of the principal of and interest on this Note will be made at
the office or agency of the Trustee maintained for that purpose in The City of
New York.

          Reference is hereby made to the further provisions of this Note set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

          Unless the certificate of authentication hereon has been executed by
the Trustee or by an authenticating agent on behalf of the Trustee by manual
signature, this Note shall not be entitled to any benefit under the Indenture or
be valid or obligatory for any purpose.


                                        2

<PAGE>

          IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed under its corporate seal.

Dated: August 2, 2006

                                        CITIGROUP INC.


                                        By:
                                            ------------------------------------
                                        Title: Chief Financial Officer


ATTEST:


By:
    ---------------------------------
Title: Assistant Secretary


                                        3

<PAGE>

          This is one of the Notes of the series issued under the
within-mentioned Indenture.

Dated: August 2, 2006

                                        THE BANK OF NEW YORK,
                                        as Trustee


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------

                                        -or-


                                        CITIBANK, N.A.,
                                        as Authenticating Agent


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        4

<PAGE>

          This Note is one of a duly authorized issue of Securities of the
Company (the "Notes"), issued and to be issued in one or more series under the
Indenture, dated as of March 15, 1987 (as amended and supplemented to date, the
"Indenture"), between the Company and The Bank of New York, as Trustee (the
"Trustee", which term includes any successor trustee under the Indenture), to
which Indenture and all indentures supplemental thereto reference is hereby made
for a statement of the respective rights, limitations of rights, duties and
immunities thereunder of the Company, the Trustee and the holders of the Notes
and of the terms upon which the Notes are, and are to be, authenticated and
delivered. This Note is one of the series designated on the face hereof,
initially limited in aggregate principal to $1,000,000,000.

          If an event of default (as defined in the Indenture) with respect to
Notes of this series shall occur and be continuing, the principal of the Notes
of this series may be declared due and payable in the manner and with the effect
provided in the Indenture.

          The Indenture contains provisions for defeasance at any time of the
entire indebtedness of this Note upon compliance by the Company with certain
conditions set forth in Sections 11.03 and 11.04 thereof, which provisions apply
to this Note.

          The Indenture contains provisions permitting the Company and the
Trustee, without the consent of the holders of the Securities, to establish,
among other things, the form and terms of any series of Securities issuable
thereunder by one or more supplemental indentures, and, with the consent of the
holders of not less than 66 2/3% in aggregate principal amount of Securities at
the time outstanding which are affected thereby, to modify the Indenture or any
supplemental indenture or the rights of the holders of Securities of such series
to be affected, provided that no such modification will (i) extend the fixed
maturity of any Securities, reduce the rate or extend the time of payment of
interest thereon, reduce the principal amount thereof or the premium, if any,
thereon, reduce the amount of the principal of Original Issue Discount
Securities payable on any date, change the currency in which Securities are
payable, or impair the right to institute suit for the enforcement of any such
payment on or after the maturity thereof, without the consent of the holder of
each Security so affected, or (ii) reduce the aforesaid percentage of Securities
of any series the consent of the holders of which is required for any such
modification without the consent of the holders of all Securities of such series
then outstanding, or (iii) modify, without the written consent of the Trustee,
the rights, duties or immunities of the Trustee.

          No reference herein to the Indenture and no provision of this Note or
of the Indenture shall alter or impair the obligation of the Company, which is
absolute and unconditional, to pay the principal of and interest on this Note at
the times, place and rate, and in the coin or currency, herein prescribed.

          This Note is a Global Security registered in the name of a nominee of
the Depository. This Note is exchangeable for Notes registered in the name of a
person other than the Depository or its nominee only in the limited
circumstances hereinafter described. Unless and until it is exchanged in whole
or in part for definitive Notes in certificated form, this Note may not be


                                        5

<PAGE>

transferred except as a whole by the Depository to a nominee of the Depository
or by a nominee of the Depository to the Depository or another nominee of the
Depository.

          The Notes represented by this Global Security are exchangeable for
definitive Notes in certificated form of like tenor as such Notes in
denominations of $100,000 and whole multiples of $1,000 in excess thereof only
if (i) the Depository notifies the Company that it is unwilling or unable to
continue as Depository for the Notes or (ii) the Depository ceases to be a
clearing agency registered under the Securities Exchange Act of 1934, as
amended, or (iii) the Company in its sole discretion decides to allow the Notes
to be exchanged for definitive Notes in registered form. Any Notes that are
exchangeable pursuant to the preceding sentence are exchangeable for
certificated Notes issuable in authorized denominations and registered in such
names as the Depository shall direct. As provided in the Indenture and subject
to certain limitations therein set forth, the transfer of definitive Notes in
certificated form is registrable in the register maintained by the Company in
The City of New York for such purpose, upon surrender of the definitive Note for
registration of transfer at the office or agency of the registrar, duly endorsed
by, or accompanied by a written instrument of transfer in form satisfactory to
the Company and the registrar duly executed by, the holder thereof or his
attorney duly authorized in writing, and thereupon one or more new Notes of this
series and of like tenor, of authorized denominations and for the same aggregate
principal amount, will be issued to the designated transferee or transferees.
Subject to the foregoing, this Note is not exchangeable, except for a Global
Security or Global Securities of this issue of the same principal amount to be
registered in the name of the Depository or its nominee.

          No service charge shall be made for any such registration of transfer
or exchange, but the Company may require payment of a sum sufficient to cover
any tax or other governmental charge payable in connection therewith.

          Prior to due presentment of this Note for registration of transfer,
the Company, the Trustee and any agent of the Company or the Trustee may treat
the Person in whose name this Note is registered as the owner hereof for all
purposes, whether or not this Note be overdue, and neither the Company, the
Trustee nor any such agent shall be affected by notice to the contrary.

          The Company will pay additional amounts ("Additional Amounts") to the
beneficial owner of any Note that is a non-United States person in order to
ensure that every net payment on such Note will not be less, due to payment of
U.S. withholding tax, than the amount then due and payable. For this purpose, a
"net payment" on a Note means a payment by the Company or a paying agent,
including payment of principal and interest, after deduction for any present or
future tax, assessment or other governmental charge of the United States. These
Additional Amounts will constitute additional interest on the Note.

          The Company will not be required to pay Additional Amounts, however,
in any of the circumstances described in items (1) through (13) below.


                                        6

<PAGE>

     (1)  Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is imposed or withheld solely by reason of the beneficial
          owner:

          (a)  having a relationship with the United States as a citizen,
               resident or otherwise;

          (b)  having had such a relationship in the past or

          (c)  being considered as having had such a relationship.

     (2)  Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is imposed or withheld solely by reason of the beneficial
          owner:

          (a)  being treated as present in or engaged in a trade or business in
               the United States;

          (b)  being treated as having been present in or engaged in a trade or
               business in the United States in the past or

          (c)  having or having had a permanent establishment in the United
               States.

     (3)  Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is imposed or withheld in whole or in part by reason of
          the beneficial owner being or having been any of the following (as
          such terms are defined in the Internal Revenue Code of 1986, as
          amended):

          (a)  personal holding company;

          (b)  foreign personal holding company;

          (c)  foreign private foundation or other foreign tax-exempt
               organization;

          (d)  passive foreign investment company;

          (e)  controlled foreign corporation or

          (f)  corporation which has accumulated earnings to avoid United States
               federal income tax.

     (4)  Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is imposed or withheld solely by reason of the beneficial
          owner owning or having owned, actually or constructively, 10 percent
          or more of the total combined voting power of all classes of stock of
          the Company entitled to vote or by reason of the beneficial owner
          being a bank that has invested in a Note as an extension of credit in
          the ordinary course of its trade or business.

For purposes of items (1) through (4) above, "beneficial owner" means a
fiduciary, settlor, beneficiary, member or shareholder of the holder if the
holder is an estate, trust, partnership, limited liability company, corporation
or other entity, or a person holding a power over an estate or trust
administered by a fiduciary holder.


                                        7

<PAGE>

     (5)  Additional Amounts will not be payable to any beneficial owner of a
          Note that is a:

          (a)  fiduciary;

          (b)  partnership;

          (c)  limited liability company or

          (d)  other fiscally transparent entity

          or that is not the sole beneficial owner of the Note, or any portion
          of the Note. However, this exception to the obligation to pay
          Additional Amounts will only apply to the extent that a beneficiary or
          settlor in relation to the fiduciary, or a beneficial owner or member
          of the partnership, limited liability company or other fiscally
          transparent entity, would not have been entitled to the payment of an
          Additional Amount had the beneficiary, settlor, beneficial owner or
          member received directly its beneficial or distributive share of the
          payment.

     (6)  Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is imposed or withheld solely by reason of the failure of
          the beneficial owner or any other person to comply with applicable
          certification, identification, documentation or other information
          reporting requirements. This exception to the obligation to pay
          Additional Amounts will only apply if compliance with such reporting
          requirements is required by statute or regulation of the United States
          or by an applicable income tax treaty to which the United States is a
          party as a precondition to exemption from such tax, assessment or
          other governmental charge.

     (7)  Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is collected or imposed by any method other than by
          withholding from a payment on a Note by the Company or a paying agent.

     (8)  Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is imposed or withheld by reason of a change in law,
          regulation, or administrative or judicial interpretation that becomes
          effective more than 15 days after the payment becomes due or is duly
          provided for, whichever occurs later.

     (9)  Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is imposed or withheld by reason of the presentation by
          the beneficial owner of a Note for payment more than 30 days after the
          date on which such payment becomes due or is duly provided for,
          whichever occurs later.

     (10) Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any:


                                        8

<PAGE>

          (a)  estate tax;

          (b)  inheritance tax;

          (c)  gift tax;

          (d)  sales tax;

          (e)  excise tax;

          (f)  transfer tax;

          (g)  wealth tax;

          (h)  personal property tax or

          (i)  any similar tax, assessment, withholding, deduction or other
               governmental charge.

     (11) Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment, or other governmental
          charge required to be withheld by any paying agent from a payment of
          principal or interest on a Note if such payment can be made without
          such withholding by any other paying agent.

     (12) Additional amounts will not be payable if a payment on a Note is
          reduced as a result of any tax, assessment or other governmental
          charge that is required to be made pursuant to any European Union
          directive on the taxation of savings income or any law implementing or
          complying with, or introduced to conform to, any such directive.

     (13) Additional Amounts will not be payable if a payment on a Note is
          reduced as a result of any combination of items (1) through (12)
          above.

          Except as specifically provided herein, the Company will not be
required to make any payment of any tax, assessment or other governmental charge
imposed by any government or a political subdivision or taxing authority of such
government.

          As used in this Note, "United States person" means:

          (a)  any individual who is a citizen or resident of the United States;

          (b)  any corporation, partnership or other entity created or organized
               in or under the laws of the United States;

          (c)  any estate if the income of such estate falls within the federal
               income tax jurisdiction of the United States regardless of the
               source of such income and

          (d)  any trust if a United States court is able to exercise primary
               supervision over its administration and one or more United States
               persons have the authority to control all of the substantial
               decisions of the trust.

          Additionally, "non-United States person" means a person who is not a
United States person, and "United States" means the states of the United States
of America and the District of Columbia, but excluding its territories and its
possessions.


                                        9

<PAGE>

          Except as provided below, the Notes may not be redeemed prior to
maturity.

     (1)  The Company may, at its option, redeem the Notes if:

          (a)  the Company becomes or will become obligated to pay Additional
               Amounts as described above;

          (b)  the obligation to pay Additional Amounts arises as a result of
               any change in the laws, regulations or rulings of the United
               States, or an official position regarding the application or
               interpretation of such laws, regulations or rulings, which change
               is announced or becomes effective on or after July 26, 2006 and

          (c)  the Company determines, in its business judgment, that the
               obligation to pay such Additional Amounts cannot be avoided by
               the use of reasonable measures available to it, other than
               substituting the obligor under the Notes or taking any action
               that would entail a material cost to the Company.

     (2)  The Company may also redeem the Notes, at its option, if:

          (a)  any act is taken by a taxing authority of the United States on or
               after July 26, 2006, whether or not such act is taken in relation
               to the Company or any affiliate, that results in a substantial
               probability that the Company will or may be required to pay
               Additional Amounts as described above;

          (b)  the Company determines, in its business judgment, that the
               obligation to pay such Additional Amounts cannot be avoided by
               the use of reasonable measures available to it, other than
               substituting the obligor under the Notes or taking any action
               that would entail a material cost to the Company and

          (c)  the Company receives an opinion of independent counsel to the
               effect that an act taken by a taxing authority of the United
               States results in a substantial probability that the Company will
               or may be required to pay the Additional Amounts described under
               above, and delivers to the Trustee a certificate, signed by a
               duly authorized officer, stating that based on such opinion the
               Company is entitled to redeem the Notes pursuant to their terms.

Any redemption of the Notes as set forth in clauses (1) or (2) above shall be in
whole, and not in part, and will be made at a redemption price equal to 100% of
the principal amount of the Notes Outstanding plus accrued interest thereon to
the date of redemption. Holders shall be given not less than 30 days nor more
than 60 days prior notice by the Trustee of the date fixed for such redemption.

          All terms used in this Note which are defined in the Indenture shall
have the meanings assigned to them in the Indenture. The Notes are governed by
the laws of the State of New York.


                                       10