<PAGE>

                                                                    Exhibit 4.01

THIS NOTE IS A GLOBAL NOTE WITHIN THE MEANING OF THE INDENTURE HEREINAFTER
REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE THEREOF.
UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR NOTES IN CERTIFICATED
FORM, THIS NOTE MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITORY TRUST
COMPANY, A NEW YORK CORPORATION ("DTC"), TO A NOMINEE OF DTC OR BY DTC OR ANY
SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR
DEPOSITARY. UNLESS THIS NOTE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF DTC
TO CITIGROUP FUNDING INC. OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR
PAYMENT, AND ANY NOTE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH
OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT
IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), 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.

No. R-1                                           INITIAL PRINCIPAL AMOUNT
CUSIP: 17308C 61 9                                REPRESENTED $42,000,000
ISIN: US17308C6194                                representing 4,200,000 Notes
                                                  ($10 per Note)

                             CITIGROUP FUNDING INC.
 Stock Market Upturn Notes(SM) Based Upon the S&P 500(R) Index Due July 12, 2007

      Citigroup Funding Inc., a Delaware corporation (hereinafter referred to as
the "Company," which term includes any successor corporation under the Indenture
herein referred to), for value received and on condition that this Note is not
redeemed by the Company prior to July 12, 2007 (the "Stated Maturity Date"),
hereby promises to pay to CEDE & CO., or its registered assigns, the Maturity
Payment (as defined below), on the Stated Maturity Date. This Note will not bear
interest, is not subject to any sinking fund, is not subject to redemption at
the option of the holder thereof prior to the Stated Maturity Date, and is not
subject to the defeasance provisions of the Indenture. The payments due on this
Note are fully and unconditionally guaranteed by Citigroup Inc., a Delaware
corporation (the "Guarantor").

      Payment of the Maturity Payment with respect to this Note shall be made
upon presentation and surrender of this Note at the corporate trust office of
the Trustee in the Borough of Manhattan, The City and State of New York, in such
coin or currency of the United States as at the time of payment is legal tender
for payment of public and private debts.

      This Note is one of the series of 4,200,000 Stock Market Upturn Notes(SM)
Based Upon the S&P 500(R) Index Due July 12, 2007 (the "Notes").

<PAGE>


INTEREST

      The Notes do not bear interest. No payments on the Notes will be made
until the Stated Maturity Date.

PAYMENT AT MATURITY

      On the Stated Maturity Date, holders of the Notes will receive for each
Note the Maturity Payment described below.

DETERMINATION OF THE MATURITY PAYMENT

      The Maturity Payment for each Note equals the sum of the initial principal
amount of $10 per Note plus the Index Return Amount.

      The "Index Return Amount" is calculated as follows:

      -     If the Index Return is positive, the Index Return Amount will equal
            the product of:

                 $10 * Upside Participation Rate * Index Return.

      -     If the Index Return is negative, the Index Return Amount will equal
            the product of:

                               $10 * Index Return

      -     If the Index Return is zero, the Index Return Amount will be zero.

      The "Index Return" equals:

                          Ending Value - Starting Value
                                 Starting Value

      provided that the Index Return will be subject to a cap of 7.7%.

      The "Upside Participation Rate" is 200%.

      The "Starting Value" is 1301.61, the closing value of the Index on
          March 27, 2006.

      The "Ending Value" will be the closing value of the Index on the third
          Index Business Day before the Stated Maturity Date.

      If no closing value of the Index is available on the third business day
before the Stated Maturity Date because of a Market Disruption Event or
otherwise, the value of the Index for that Index Business Day, unless deferred
by the calculation agent as described below, will be the arithmetic mean, as
determined by the calculation agent, of the value of the Index obtained from


                                       2
<PAGE>
as many dealers in equity securities (which may include Citigroup Global
Markets Inc. or any of the Company's other affiliates), but not exceeding three
such dealers, as will make such value available to the calculation agent. The
determination of the value of the Index by the calculation agent in the event of
a Market Disruption Event may be deferred by the calculation agent for up to
five consecutive Index Business Days on which a Market Disruption Event is
occurring, but not past the Index Business Day prior to the Stated Maturity
Date.

      An "Index Business Day" means a day, as determined by the calculation
agent, on which the Index or any successor index is calculated and published and
on which securities comprising more than 80% of the value of the Index on such
day are capable of being traded on their relevant exchanges or markets during
the one-half hour before the determination of the closing value of the Index.
All determinations made by the calculation agent will be at the sole discretion
of the calculation agent and will be conclusive for all purposes and binding on
the Company, the Guarantor and the beneficial owners of the Notes, absent
manifest error.

      A "Market Disruption Event" means, as determined by the calculation agent
in its sole discretion, the occurrence or existence of any suspension of or
limitation imposed on trading (by reason of movements in price exceeding limits
permitted by any relevant exchange or market or otherwise) of, or the
unavailability, through a recognized system of public dissemination of
transaction information, for a period longer than two hours, or during the
one-half hour period preceding the close of trading, on the applicable exchange
or market, of accurate price, volume or related information in respect of (a)
stocks which then comprise 20% or more of the value of the Index or any
successor index, (b) any options or futures contracts, or any options on such
futures contracts relating to the Index or any successor index, or (c) any
options or futures contracts relating to stocks which then comprise 20% or more
of the value of the Index or any successor index on any exchange or market if,
in each case, in the determination of the calculation agent, any such
suspension, limitation or unavailability is material. For the purpose of
determining whether a Market Disruption Event exists at any time, if trading in
a security included in the Index is materially suspended or materially limited
at that time, then the relevant percentage contribution of that security to the
value of the Index will be based on a comparison of the portion of the value of
the Index attributable to that security relative to the overall value of the
Index, in each case immediately before that suspension or limitation.

DISCONTINUANCE OF THE S&P 500(R) Index

      If Standard & Poor's ("S&P") discontinues publication of the Index or if
it or another entity publishes a successor or substitute index that the
calculation agent determines, in its sole discretion, to be comparable to the
Index, then the value of the Index will be determined by reference to the value
of that index, which we refer to as a "successor index."

      Upon any selection by the calculation agent of a successor index, the
calculation agent will cause notice to be furnished to the Company and the
Trustee, who will provide notice of the selection of the successor index to the
registered holders of the Notes.

      If S&P discontinues publication of the Index and a successor index is not
selected by the calculation agent or is no longer published on any date of
determination of the value of the


                                       3
<PAGE>

Index, the value to be substituted for the Index for that date will be a value
computed by the calculation agent for that date in accordance with the
procedures last used to calculate the Index prior to any such discontinuance.

      If S&P discontinues publication of the Index prior to the determination of
the Index Return Amount and the calculation agent determines that no successor
index is available at that time, then on each Index Business Day until the
earlier to occur of (a) the determination of the Index Return Amount and (b) a
determination by the calculation agent that a successor index is available, the
calculation agent will determine the value that is to be used in computing the
value of the Index as described in the preceding paragraph. The calculation
agent will cause notice of those daily closing values to be published not less
often than once each month in The Wall Street Journal (or another newspaper of
general circulation).

      If a successor index is selected or the calculation agent calculates a
value as a substitute for the Index as described above, the successor index or
value will be substituted for the Index for all purposes, including for purposes
of determining whether an Index Business Day or Market Disruption Event occurs.

      All determinations made by the calculation agent will be at the sole
discretion of the calculation agent and will be conclusive for all purposes and
binding on the Company, the Guarantor and the beneficial owners of the Notes,
absent manifest error.

ALTERATION OF METHOD OF CALCULATION

      If at any time the method of calculating the Index or a successor index is
changed in any material respect, or if the Index or any successor index is in
any other way modified so that the value of the Index or the successor index
does not, in the opinion of the calculation agent, fairly represent the value of
that index had the changes or modifications not been made, then, from and after
that time, the calculation agent will, at the close of business in New York, New
York, make those adjustments as, in the good faith judgment of the calculation
agent, may be necessary in order to arrive at a calculation of a value of a
stock index comparable to the Index or the successor index as if the changes or
modifications had not been made, and calculate the value of the index with
reference to the Index or the successor index. Accordingly, if the method of
calculating the Index or any successor index is modified so that the value of
the Index or the successor index is a fraction or a multiple of what it would
have been if it had not been modified, then the calculation agent will adjust
that index in order to arrive at a value of the index as if it had not been
modified.

GENERAL

      This Note is one of a duly authorized issue of debt securities of the
Company (the "Debt Securities"), issued and to be issued in one or more series
under a Senior Debt Indenture, dated as of June 1, 2005 (the "Indenture"), among
the Company, the Guarantor and The Bank of New York, as trustee (the "Trustee",
which term includes any successor trustee under the Indenture), to which
Indenture reference is hereby made for a statement of the respective rights,
limitations of rights, duties and immunities thereunder of the Company, the
Guarantor, the Trustee and the


                                       4
<PAGE>

holders of the Notes, and the terms upon which the Notes are, and are to be,
authenticated and delivered.

      If an Event of Default with respect to the Notes shall have occurred and
be continuing, the amount declared due and payable upon any acceleration of the
Notes permitted by the Indenture will be determined by the calculation agent and
will be equal to, with respect to this Note, the Maturity Payment calculated as
though the Stated Maturity Date of this Note were the date of early repayment.
In case of default at the Stated Maturity Date of this Note, this Note shall
bear interest, payable upon demand of the beneficial owners of this Note in
accordance with the terms of the Note, from and after the Stated Maturity Date
through the date when payment of such amount has been made or duly provided for,
at the rate of 5.5% per annum on the unpaid amount due.

      The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the Guarantor and the rights of the holders of the Debt Securities
of each series to be affected under the Indenture at any time by the Company,
the Guarantor and a majority in aggregate principal amount of the Debt
Securities at the time Outstanding of each series affected thereby. The
Indenture also contains provisions permitting the holders of specified
percentages in aggregate principal amount of the Debt Securities of any series
at the time Outstanding, on behalf of the holders of all Debt Securities of such
series, to waive compliance by the Company and the Guarantor with certain
provisions of the Indenture and certain past defaults under the Indenture and
their consequences. Any such consent or waiver by the holder of this Note shall
be conclusive and binding upon such holder and upon all future holders of this
Note and of any Note issued upon the registration of transfer hereof or in
exchange herefor or in lieu hereof, whether or not notation of such consent or
waiver is made upon this Note.

      The holder of this Note may not enforce such holder's rights pursuant to
the Indenture or the Notes except as provided in the Indenture. 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 and the Guarantor to pay the
Maturity Payment with respect to this Note, and to pay any interest on any
overdue amount thereof at the time, place and rate, and in the coin or currency,
herein prescribed.

      All terms used in this Note which are defined in the Indenture but not in
this Note shall have the meanings assigned to them in the Indenture.

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


                                       5
<PAGE>



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

                                     CITIGROUP FUNDING INC.


                                     By: /s/ Geoffrey S. Richards
                                         --------------------------
                                         Name:   Geoffrey S. Richards
                                         Title:  Vice President and Assistant
                                         Treasurer



Corporate Seal
Attest:

By:  /s/ Douglas C. Turnbull
     -------------------------------------
     Name:  Douglas C. Turnbull
     Title: Assistant Secretary

Dated March 30, 2006

CERTIFICATE OF AUTHENTICATION
      This is one of the Notes referred to in
      the within-mentioned Indenture.

The Bank of New York,
as Trustee

By:  /s/ Geovanni Barris
     -------------------------------------
     Authorized Signatory


                                       6