<PAGE>   1


                                                                    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.
                  FLOATING RATE NOTES DUE MAY 30, 2003
REGISTERED                                                           REGISTERED

                                                         CUSIP: 172967 [___ __]
                                                       ISIN: US172967 [___ ___]
                                                   Common Code: [_____________]

No. R-                                                                        $

            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 May 30, 2003 and to pay interest thereon from and including May
30, 2001 or from the most recent Interest Payment Date to which interest has
been paid or duly provided for, quarterly, on February 28, May 30, August 30 and
November 30 of each year, commencing August 30, 2001, at the rate per annum for
each Interest Period of three-month LIBOR plus 0.08%, determined as provided
herein, 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 Business Day immediately preceding such
Interest Payment Date.
<PAGE>   2
            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 the actual number
of days elapsed in an Interest Period and a 360-day year. Dollar amounts
resulting from such calculation will be rounded to the nearest cent, with
one-half cent being rounded upward. An "Interest Period" shall be the period
from and including an Interest Payment Date (or from May 30, 2001 in the case of
the first Interest Payment Date) to and including the day immediately preceding
the next Interest Payment Date.

            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 the
Maturity of the Notes will be the next succeeding Business Day (unless that day
falls in the next calendar month, in which case such date will be the first
preceding Business Day). 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.

            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.

            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.


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<PAGE>   3
            IN WITNESS WHEREOF, the Company has caused this instrument to be
duly executed under its corporate seal.

Dated:  May 30, 2001

                                           CITIGROUP INC.



                                           By:_________________________________
                                              Title:  Treasurer



ATTEST:

By:___________________________
Assistant Secretary


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<PAGE>   4
            This is one of the Notes of the series issued under the
within-mentioned Indenture.

Dated:  May 30, 2001

                                           THE BANK OF NEW YORK,
                                           as Trustee


                                           By:_________________________________
                                              Name:
                                              Title:


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<PAGE>   5
      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 $2,500,000,000.

      This Note will bear interest for each Interest Period at a rate determined
by The Bank of New York, acting as Calculation Agent. The interest rate on this
Note for a particular Interest Period will be a per annum rate equal to LIBOR as
determined on the related Interest Determination Date plus 0.08%. The Interest
Determination Date for an Interest Period will be the second London business day
preceding such Interest Period. Promptly upon determination, the Calculation
Agent will inform the Trustee and the Company of the interest rate for the next
Interest Period. Absent manifest error, the determination of the interest rate
by the Calculation Agent shall be binding and conclusive on the holders of
Notes, the Trustee and the Company.

      A London business day is a day on which dealings in deposits in U.S.
dollars are transacted in the London interbank market.

      On any Interest Determination Date, LIBOR will be equal to the offered
rate for deposits in U.S. dollars having an index maturity of three months for
the next Interest Period, in amounts of at least $1,000,000, as such rate
appears on Telerate Page 3750 at approximately 11:00 a.m., London time, on such
Interest Determination Date. If the Telerate Page 3750 is replaced by another
service or ceases to exist, the Calculation Agent will use the replacing service
or such other service that may be nominated by the British Bankers' Association
for the purpose of displaying London interbank offered rates for U.S. dollar
deposits.

      If no offered rate appears on Telerate Page 3750 on an Interest
Determination Date at approximately 11:00 a.m., London time, then the
Calculation Agent (after consultation with the Company) will select four major
banks in the London interbank market and shall request each of their principal
London offices to provide a quotation of the rate at which three-month deposits
in U.S. dollars in amounts of at least $1,000,000 are offered by it to prime
banks in the London interbank market, on that date and at that time, that is
representative of single transactions at that time. If at least two quotations
are provided, LIBOR will be the arithmetic average of the quotations provided.
Otherwise, the Calculation Agent will select three major banks in New York City
and shall request each of them to provide a quotation of the rate offered by
them at approximately 11:00 a.m., New York City time, on the Interest
Determination Date for loans in U.S. dollars to leading European banks having an
index maturity of three months for the applicable Interest Period in an amount
of at least $1,000,000 that is representative of single transactions at that
time. If three quotations are provided, LIBOR will be the arithmetic average


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<PAGE>   6
of the quotations provided. Otherwise, the rate of LIBOR for the next Interest
Period will be set equal to the rate of LIBOR for the current Interest Period.

      The interest rate in effect for this Note for the first Interest Period of
May 30, 2001 to August 29, 2001 shall be 4.11%.

      Upon request from any Noteholder, the Calculation Agent will provide the
interest rate in effect on this Note for the current Interest Period and, if it
has been determined, the interest rate to be in effect for the next Interest
Period.

      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
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.


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<PAGE>   7
      The Notes represented by this Global Security are exchangeable for
definitive Notes in certificated form of like tenor as such Notes in
denominations of $1,000 and integral multiples 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.

      (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:


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<PAGE>   8
            (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 solely by reason of the
            beneficial owner being or having been a:

            (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.

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.

      (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


                                       8
<PAGE>   9
            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:

            (a)   estate tax;

            (b)   inheritance tax;

            (c)   gift tax;

            (d)   sales tax;

            (e)   excise tax;

            (f)   transfer tax;

            (g)   wealth tax;


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<PAGE>   10
            (h)   personal property tax or

            (i)   any similar tax, assessment 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 United States of America,
including the States and the District of Columbia, its territories, its
possessions and other areas within its jurisdiction.

      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


                                       10
<PAGE>   11
                  rulings, which change is announced or becomes effective on or
                  after May 23, 2001 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 May 23, 2001, 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.


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