ONE GAS, INC. SUPPLEMENTAL INDENTURE NO. 8 $250,000,000 5.10% Senior Notes due 2029

Exhibit 4.2

ONE GAS, INC.

SUPPLEMENTAL INDENTURE NO. 8

$250,000,000 5.10% Senior Notes due 2029

THIS SUPPLEMENTAL INDENTURE NO. 8, dated as of August 12, 2024 (this “Supplemental Indenture”), between ONE GAS, INC., an Oklahoma corporation (the “Company”), and U.S. BANK TRUST COMPANY, NATIONAL ASSOCIATION (successor in interest to U.S. Bank National Association), a national banking association, as trustee (the “Trustee”).

RECITALS OF THE COMPANY:

WHEREAS, the Company has heretofore executed and delivered to the Trustee an Indenture, dated as of January 27, 2014, by and between the Company and the Trustee (the “Original Indenture”) (the Original Indenture, as amended and supplemented from time to time, including, without limitation, pursuant to this Supplemental Indenture, being referred to herein collectively as the “Indenture”), providing for the issuance from time to time of one or more series of Securities (as defined in the Original Indenture);

WHEREAS, Article Nine of the Original Indenture provides for various matters with respect to any series of Securities issued under the Indenture to be established in an indenture supplemental to the Original Indenture;

WHEREAS, Section 9.1(7) of the Original Indenture provides that the Company and the Trustee may enter into an indenture supplemental to the Original Indenture to establish the form or terms of Securities of any series as permitted by Sections 2.1 and 3.1 of the Original Indenture;

WHEREAS, the Company has previously issued $300,000,000 aggregate principal amount of its 5.10% Senior Notes due 2029 (the “Initial Notes”) pursuant to the terms of Supplemental Indenture No. 7, dated as of December 13, 2023, between the Company and the Trustee;

WHEREAS, Section 3.1 of the Original Indenture provides, among other things, that not all Securities of any one series need be issued at the same time, and that, unless otherwise provided, a series may be reopened for issuances of additional Securities of such series, subject to conditions set forth in the Original Indenture;

WHEREAS, pursuant to this Supplemental Indenture, the Company is issuing $250,000,000 in aggregate principal amount of its 5.10% Senior Notes due 2029 as “Additional Notes” of such series (together with the Initial Notes, the “Notes”); and

WHEREAS, all the conditions and requirements necessary to make this Supplemental Indenture, when duly executed and delivered, a valid and binding agreement in accordance with its terms and for the purposes herein expressed, have been performed and fulfilled.

NOW THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH

For and in consideration of the premises and the issuance of the series of Securities provided for herein, the Company and the Trustee mutually covenant and agree for the equal and proportionate benefit of the respective Holders of the Securities of each such series as follows:

ARTICLE I

RELATION TO INDENTURE; DEFINITIONS; RULES OF CONSTRUCTION

SECTION 1.1 Relation to Indenture. This Supplemental Indenture constitutes an integral part of the Indenture.

SECTION 1.2 Definitions. For all purposes of this Supplemental Indenture, the following terms shall have the respective meanings set forth in this Section.

“Definitive Note” means a certificated Note that does not include the legend prescribed in Section 2.4 of the Original Indenture.

“Depository” means The Depository Trust Company, its nominees and their respective successors.

“Global Notes” means one or more Securities evidencing all or part of the Securities to be issued as Book-Entry Securities, issued to the Depositary in accordance with Section 3.1 of the Original Indenture and bearing the legend prescribed in Section 2.4 of the Original Indenture.

“Notes” shall have the meaning set forth in Section 2.1 hereof.

“Notes Custodian” means the custodian with respect to a Global Note (as appointed by the Depository) or any successor person thereto, who will initially be the Trustee.

“Participant” means members of, or participants in, the Depository.

SECTION 1.3 Rules of Construction. For all purposes of this Supplemental Indenture:

(a) capitalized terms used herein without definition shall have the meanings assigned thereto in the Original Indenture;

(b) all references herein to Articles and Sections, unless otherwise specified, refer to the corresponding Articles and Sections of this Supplemental Indenture;

(c) terms “herein,” “hereof,” “hereunder” and other words of similar import refer to this Supplemental Indenture; and

(d) in the event of a conflict with the definition of terms in the Original Indenture, the definitions in this Supplemental Indenture shall control.

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ARTICLE II

THE SECURITIES

SECTION 2.1 Creation of the Additional Notes. As of the date hereof, the Company hereby creates and issues the Additional Notes under this Supplemental Indenture. The Additional Notes shall be consolidated with, and shall form part of a single series with, the Initial Notes and shall have the same terms and conditions as the Initial Notes in all respects, except for the issue date, the issue price, the payment of interest accruing prior to the issue date of the Additional Notes and the first Interest Payment Date (as defined below).

SECTION 2.2 Initial Principal Amount. The Additional Notes will be initially issued in an aggregate principal amount of $250,000,000.

SECTION 2.3 Form and Dating.

(a) General. The Additional Notes and the Trustee’s certificate of authentication shall be substantially in the form of Exhibit A attached hereto. The Additional Notes may have notations, legends or endorsements required by law, stock exchange rule or usage. Each Additional Note shall be dated the date of its authentication. The Additional Notes shall be in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

The terms and provisions contained in the Additional Notes shall constitute, and are hereby expressly made, a part of this Supplemental Indenture, and the Company and the Trustee, by their execution and delivery of this Supplemental Indenture, expressly agree to such terms and provisions and to be bound thereby. However, to the extent any provision of the Additional Notes conflicts with the express provisions of this Supplemental Indenture, the provisions of this Supplemental Indenture shall govern and be controlling.

The Company hereby designates The Depository Trust Company as the initial depository for the Global Notes.

(b) Global Notes. The Additional Notes shall initially be issuable in whole or in part in the form of one or more Global Notes. Such Global Notes (i) shall be deposited with, or on behalf of, the Depository, which shall act as depository with respect to the Additional Notes, (ii) shall bear the legend prescribed by Section 2.4 of the Original Indenture, (iii) may be exchanged in whole or in part upon the terms and subject to the conditions provided in Section 3.5 of the Original Indenture and (iv) shall otherwise be subject to the applicable provisions of the Indenture.

(c) Book-Entry Provisions. This Section 2.3(c) shall apply only to a Global Note deposited with or on behalf of the Depository. The Company shall execute and the Trustee shall, in accordance with this Section 2.3(c) and pursuant to a Company Order, authenticate and deliver initially one or more Global Notes that (a) shall be registered in the name of the Depository for such Global Note or Global Notes or the nominee of such Depository and (b) shall be delivered by the Trustee to such Depository or pursuant to such Depository’s instructions or held by the Trustee as Notes Custodian.

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Participants shall have no rights under the Indenture with respect to any Global Note held on their behalf by the Depository or by the Trustee as Notes Custodian or under such Global Note, and the Depository may be treated by the Company, the Trustee and any agent of the Company or the Trustee as the absolute owner of such Global Note for all purposes whatsoever. Notwithstanding the foregoing, nothing herein shall prevent the Company, the Trustee or any agent of the Company or the Trustee from giving effect to any written certification, proxy or other authorization furnished by the Depository or impair, as between the Depository and its Participants, the operation of customary practices of such Depository governing the exercise of the rights of a holder of a beneficial interest in any Global Note.

(d) Definitive Notes. Except as provided in Section 2.4 hereof, owners of beneficial interests in Global Notes will not be entitled to have the notes registered in their names, will not be entitled to receive physical delivery of certificated Additional Notes and will not be considered the owners or holders of the Global Notes under the Indenture.

(e) Cancellation of Global Note. At such time as all beneficial interests in a Global Note have either been exchanged for Definitive Notes, transferred, redeemed, repurchased or canceled, such Global Note shall be returned by the Depository to the Trustee for cancellation or retained and canceled by the Trustee. At any time prior to such cancellation, if any beneficial interest in a Global Note is exchanged for Definitive Notes, transferred in exchange for an interest in another Global Note, redeemed, repurchased or canceled, the principal amount of Additional Notes represented by such Global Note shall be reduced and an adjustment shall be made on the books and records of the Trustee (if it is then the Notes Custodian for such Global Note) with respect to such Global Note, by the Trustee or the Notes Custodian, to reflect such reduction.

SECTION 2.4 Definitive Notes.

(a) A Global Note deposited with the Depository or with the Trustee as Notes Custodian pursuant to Section 2.3 shall be transferred to the beneficial owners thereof in the form of Definitive Notes in an aggregate principal amount equal to the principal amount of such Global Note, in exchange for such Global Note in the event (i) the Depository (A) notifies the Company that the Depository is no longer willing or able to act as a depositary or clearing system for such Global Notes or (B) ceases to be a “clearing agency” registered under the Securities Exchange Act of 1934, as amended, and, in either event, a successor depositary or clearing system is not appointed by the Company within 90 days of such notice or cessation, (ii) the Company, in its sole discretion, notifies the Trustee in writing that it elects to cause the issuance of Definitive Notes under the Indenture, or (iii) upon the occurrence and continuation of an Event of Default and the Depository notifies the Trustee of its decision to exchange the Global Note for Definitive Notes.

(b) Any Global Note that is transferable to the beneficial owners thereof pursuant to this Section 2.4 shall be surrendered by the Depository to the Trustee, to be so transferred, in whole or from time to time in part, without charge, and upon Company Order the Trustee shall authenticate and deliver, upon such transfer of each portion of such Global Note, an equal aggregate principal amount of Definitive Notes of authorized denominations. Any portion of a Global Note transferred pursuant to this Section 2.4 shall be executed, authenticated and delivered only in denominations of $2,000 of principal amount and any integral multiple of $1,000 in excess thereof and registered in such names as the Depository shall direct.

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(c) The registered Holder of a Global Note may grant proxies and otherwise authorize any Person, including Participants and Persons that may hold interests through Participants, to take any action which a Holder is entitled to take under the Indenture or the Additional Notes as provided therein.

(d) In the event of the occurrence of any of the events specified in Section 2.4(a)(i), (ii) or (iii), the Company will promptly make available to the Trustee a reasonable supply of Definitive Notes in fully registered form without interest coupons.

SECTION 2.5 Stated Maturity. The Stated Maturity of the Additional Notes shall be April 1, 2029.

SECTION 2.6 Interest and Interest Rate. The rate at which the Additional Notes shall bear interest, the date or dates from which such interest shall accrue, the interest payment dates on which any such interest shall be payable and the regular record date for any interest payable on any interest payment date, in each case, shall be as set forth in the form of Note attached hereto as Exhibit A.

SECTION 2.7 Optional Redemption. At its option, the Company may redeem the Additional Notes (taken as part of a single series with the Initial Notes), in whole or in part, at any time and from time to time, at the applicable redemption price determined as set forth in the form of Note attached hereto as Exhibit A, in accordance with the terms set forth therein and in accordance with Article XI of the Original Indenture.

ARTICLE III

MISCELLANEOUS PROVISIONS

SECTION 3.1 Ratification. The Original Indenture, as amended and supplemented from time to time, including, without limitation, as supplemented and amended by this Supplemental Indenture, is in all respects hereby adopted, ratified and confirmed.

SECTION 3.2 Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which when so executed shall be deemed an original, and all such counterparts shall together constitute but one and the same instrument.

SECTION 3.3 Governing Law. THIS SUPPLEMENTAL INDENTURE AND EACH SECURITY SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

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SECTION 3.4 Conflict with Trust Indenture Act. If any provision hereof limits, qualifies or conflicts with a provision of the Trust Indenture Act that is required under such Act to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the Trust Indenture Act that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

[Signature Page Follows]

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IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture No. 8 to be duly executed as of the day and year first above written.

[SIGNATURE PAGE TO SUPPLEMENTAL INDENTURE NO. 8]

[SIGNATURE PAGE TO SUPPLEMENTAL INDENTURE NO. 8]

Exhibit A

[FORM FACE OF NOTE]

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), 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 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.

ONE GAS, INC.

5.10% Senior Notes due 2029

ONE Gas, Inc., a corporation duly organized and existing under the laws of Oklahoma (herein called the “Company,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to, or registered assigns, the principal sum of [•], as such amount may be increased or decreased as set forth in the Schedule of Increase or Decrease in Principal Amount of Global Note attached hereto, on April 1, 2029, the maturity date, and to pay interest thereon from April 1, 2024 or from the most recent Interest Payment Date (as defined below) to which interest has been paid or duly provided for, semi-annually on April 1 and October 1 (each such date, an “Interest Payment Date”) and in each year, commencing October 1, 2024, at the rate of 5.10% per annum, until the principal hereof is paid or made available for payment, and (to the extent that the payment of such interest shall be legally enforceable) at the same rate on any overdue principal and premium and on any overdue installment of interest. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date (as defined below) for such interest, which shall be (a) the 15^th of March or 15^th of September (whether or not a Business Day), as the case may be, immediately preceding such Interest Payment Date or (b) so long as this note is a global note in book-entry form on the Business Day immediately preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date (each a “Regular Record Date”) and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such Special 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 Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

Reference is hereby made to the further provisions of this Security 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 referred to on the reverse hereof by manual signature, this Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed.

Dated: [•]

I, ▇▇▇▇▇ ▇. ▇▇▇▇▇, Vice President, Associate General Counsel and Secretary of ONE Gas, Inc., do hereby certify that ▇▇▇▇ ▇. ▇▇▇▇▇ is the duly qualified and elected Vice President and Treasurer of ONE Gas, Inc. and that the signature set forth above her name is her true signature.

Dated: [•]

[Signature Page to 2029 Global Note]

TRUSTEE’S CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated: [•]

[Signature Page to 2029 Global Note]

[REVERSE OF NOTE]

ONE GAS, INC.

5.10% Senior Notes Due 2029

This Security is one of a duly authorized issue of securities of the Company (herein called the “Securities”), issued and to be issued in one or more series under an Indenture, dated as of January 27, 2014 (the “Original Indenture”), as it may be supplemented or amended from time to time, including, without limitation, Supplemental Indenture No. 8 (herein, collectively, called the “Indenture”), between the Company and U.S. Bank Trust Company, National Association (successor in interest to U.S. Bank National Association), as trustee (herein called 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 Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof. This security is limited in aggregate principal amount to $[•].

Prior to March 1, 2029 (which is the date that is one month prior to the maturity date of the Securities) (the “Par Call Date”), the Company may redeem the Securities at its option, in whole or in part, at any time and from time to time, at a redemption price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

(1)(a) the sum of the present values of the remaining scheduled payments of principal and interest thereon discounted to the redemption date (assuming the Securities matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate (as defined below) plus 15 basis points less (b) interest accrued and unpaid thereon to the date of redemption, and

(2) 100% of the principal amount of the Securities to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the redemption date.

On or after the Par Call Date, the Company may redeem the Securities at its option, in whole or in part, at any time and from time to time, at a redemption price equal to 100% of the principal amount of the Securities being redeemed plus accrued and unpaid interest thereon to, but excluding, the redemption date.

“Treasury Rate” means, with respect to any redemption date, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the redemption date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading) (“H.15 TCM”). In determining the Treasury Rate, the Company shall select, as applicable:

(1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the redemption date to the Par Call Date (the “Remaining Life”); or

(2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields—one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life—and shall interpolate to the Par Call Date on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or

(3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the redemption date.

If on the third business day preceding the redemption date H.15 TCM is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such redemption date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date, as applicable. If there is no United States Treasury security maturing on the Par Call Date but there are two or more United States Treasury securities with a maturity date equally distant from the Par Call Date, one with a maturity date preceding the Par Call Date and one with a maturity date following the Par Call Date, the Company shall select the United States Treasury security with a maturity date preceding the Par Call Date. If there are two or more United States Treasury securities maturing on the Par Call Date or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the redemption price shall be conclusive and binding for all purposes, absent manifest error.

The redemption price will be quoted to the Trustee in writing and the Trustee shall have no duty to determine, or verify the calculation of, the redemption price.

The Original Indenture contains provisions (including in Sections 14.2 and 14.3 thereof), and such provisions shall apply to this Security, for defeasance at any time of the entire indebtedness of this Security or certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth therein.

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 rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Company and the Trustee with the consent of the Holders of not less than a majority in principal amount of the Securities at the time Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of specified percentages in principal amount of the Securities at the time Outstanding of any series, on behalf of the Holders of all Securities of such series, to waive compliance by the Company 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 Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security 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 Security.

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

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registerable in the Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Company in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Security Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities 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.

The Securities of this series are issuable only in registered form without coupons in denominations of $2,000 and whole multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, Securities of this series are exchangeable for a like aggregate principal amount of Securities of this series and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

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 Security 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 Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

This Security shall be governed by and construed in accordance with the laws of the State of New York.

INCREASES OR DECREASES IN PRINCIPAL

AMOUNT OF GLOBAL NOTE

The initial principal amount of this Global Note is $[•]. The following increases or decreases in this Global Note have been made: