Document:

<PAGE>

NOTE: REDACTED PORTIONS HAVE BEEN MARKED WITH (***). THE REDACTED PORTIONS ARE
SUBJECT TO A REQUEST FOR CONFIDENTIAL TREATMENT THAT HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION.

                                                                   EXHIBIT 10.26

                AMENDMENT TO WARRANT TO PURCHASE COMMON STOCK,
                    DATED AS OF SEPTEMBER 21, 1999, BETWEEN
                         TELLIUM, INC. ("TELLIUM") AND
                 DYNEGY GLOBAL COMMUNICATIONS, INC. ("DYNEGY")
                        (AS SUCCESSOR TO EXTANT, INC.)
                           (THE "WARRANT AGREEMENT")

     This Amendment to the Warrant Agreement is made as of November 2, 2000 by
and between Dynegy and Tellium. All capitalized terms that are used herein but
not defined shall have the meaning ascribed to them in the Warrant Agreement.

     In consideration of the mutual covenants set forth herein, and other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, and intending to be legally bound hereby, the parties agree as
follows:

     1.  Section 3(a) shall be deleted in its entirety and replaced with the
following:

         3.  Exercise of Warrant.

         (a) All of the shares subject to the Warrant (the "Warrant Shares") are
irrevocably and fully vested immediately upon execution and delivery of the
Purchase Agreement by Extant. The purchase rights represented by this Warrant as
to the vested shares are exercisable pursuant to the exercise schedule attached
hereto as Annex 1 (the "Exercise Schedule"). Such shares exercisable pursuant to
the Exercise Schedule are exercisable by the Holder in whole or in part at any
time, or from time to time, during the term hereof as described in Section 1
above, by the surrender of this Warrant and Notice of Exercise attached as Annex
II hereto duly completed and executed on behalf of the Holder, at the principal
offices of the Company (or such other office or agency of the Company as it may
designate by notice in writing to the Holder at the address of the Holder
appearing on the books of the Company), upon payment (i) in cash payable to the
Company, (ii) by wire transfer of immediately available funds, (iii) by
cancellation by the Holder of indebtedness of the Company to the Holder, or (iv)
by some combination of (i), (ii) and (iii), in each case, of the purchase price
of the shares to be purchased.

         2.  Annex I shall be deleted in its entirety and replaced with the
Annex I attached hereto.

         3.  The parties acknowledge that all of the prior amendments to the
Warrant Agreement are as follows:

             .  Amendment dated December, 1999.

             .  Supplemental Letter Agreement dated November 2, 2000 among
                Dynegy Connect, L.P., DCP Leasing L.L.C. (as Construction
                Agent), Tellium, and Dynegy, Inc.

             .  Amended and Restated Letter Agreement dated November 2, 2000
                among Dynegy Connect, L.P., Tellium, and Polaris Connect
                Statutory Trust.
<PAGE>

NOTE: REDACTED PORTIONS HAVE BEEN MARKED WITH (***). THE REDACTED PORTIONS ARE
SUBJECT TO A REQUEST FOR CONFIDENTIAL TREATMENT THAT HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION.

          4.  This Agreement may be executed in two or more counterparts, and it
shall not be necessary that the signatures of all parties hereto be contained on
any one counterpart hereof; each counterpart shall be deemed an original, but
all of which together shall constitute one and the same instrument.  Delivery of
an executed signature page of this Letter Agreement by facsimile transmission
shall be effective as delivery of a manually-executed counterpart hereof.

             [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                      -2-
<PAGE>

NOTE: REDACTED PORTIONS HAVE BEEN MARKED WITH (***). THE REDACTED PORTIONS ARE
SUBJECT TO A REQUEST FOR CONFIDENTIAL TREATMENT THAT HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION.

          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be duly executed and delivered by their respective officers thereunto duly
authorized as of the first date above written.

                                 TELLIUM, INC.

                                 By: /s/ Nicholas DeVito
                                    ---------------------------
                                    Name:  Nicholas DeVito
                                    Title: VP Business Development

                                 DYNEGY GLOBAL COMMUNICATIONS, INC.

                                 By:   /s/ Michael G. Gray
                                    ---------------------------
                                       Name:  Michael G. Gray
                                       Title: Vice President

                                 DYNEGY CONNECT, L.P.

                                 By:   /s/ Michael S. Sava
                                    ---------------------------
                                       Name:  Michael S. Sava
                                       Title: Executive Vice President

AGREED AND ACCEPTED
AS OF THE ABOVE DATE
BY THE FOLLOWING
BENEFICIAL OWNERS:

DYNEGY STRATEGIC INVESTMENTS, L.P.

   By: /s/ Gregory D. Kingsley
       ---------------------------
       Name:  Gregory D. Kingsley
       Title: Assistant Treasurer

TELSTRA HOLDINGS Pty Limited

By:_________________________________
  Name:
  Title:

                                      -3-
<PAGE>

NOTE: REDACTED PORTIONS HAVE BEEN MARKED WITH (***). THE REDACTED PORTIONS ARE
SUBJECT TO A REQUEST FOR CONFIDENTIAL TREATMENT THAT HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION.
                                                                         ANNEX I
                                                                         -------

                               EXERCISE SCHEDULE

     (* * *) of the shares subject to the Warrant (the "Warrant Shares") shall
irrevocably be exercisable immediately upon execution and delivery of the
Purchase Agreement. (* * *) of the Warrant Shares shall irrevocably be
exercisable upon delivery of an order by Dynegy and acceptance thereof by
Tellium for a least (* * *) (such order to be coincident with signed Purchase
Agreement and to include (* * *) already in Dynegy's possession for testing),
and an additional (* * *) of the Warrant Shares shall irrevocably be exercisable
upon payment therefor. (* * *) of the Warrant Shares shall irrevocably be
exercisable on delivery of one or more orders by Dynegy and acceptance thereof
by Tellium for a least (* * *) in the aggregate.

     The remaining Warrant Shares shall irrevocably be exercisable at a rate of
(* * *) for each (* * *) of products and services (including, without
limitation, the (* * *) referenced above) delivered under the Purchase Agreement
and acceptance and payment therefor and thereunder, provided that, subject to
the terms of this schedule, Authorized Purchasers purchase at least (* * *) of
products and services during the (* * *) anniversary years (as defined below)
during which the Warrant is outstanding; provided, further, that such (* * *)
purchase requirement shall not apply to (* * *). Notwithstanding the foregoing,
if Authorized Purchasers pay any (* * *) with respect to any Purchase Agreement
products to any contractor other than Tellium, such (* * *) shall be excluded in
calculating whether Authorized Purchasers accepted and paid for any (* * *)
increment of products and services for purposes of determining the
exercisability of Warrant Shares. The Warrant Shares shall irrevocably be
exercisable with respect to each such (* * *) of products and services on the
date upon which Authorized Purchasers complete payment for such (* * *) of
products and services, and not at the end of the anniversary year during which
such payment is made. Notwithstanding the foregoing, in the event that
Authorized Purchasers fail to purchase at least (* * *) of products and services
during any such anniversary year, (i) the exercisability of previously
exercisable Warrant Shares shall be unaffected, and (ii) Warrant Shares shall
continue to irrevocably exercisable at the rate of (* * *) for each (* * *) of
products and services purchased by Authorized Purchasers pursuant to the
Purchase Agreement, so long as the quotient obtained by dividing (a) the
aggregate amount purchased by Authorized Purchasers for products and services
under the Purchase Agreement during such year and each prior year during the
term of his Warrant (collectively, the "Completed Years") by (b) the Completed
Years, is equal to or in excess of (* * *), For purposes of this exercise
schedule, the term "anniversary year" is based on the effective date of the
Purchase Agreement.

     Example 1: If Dynegy (and its Authorized Purchasers) purchases products and
services during anniversary years (* * *) equal to (* * *), (* * *), (* * *), (*
* *) and (* * *), respectively, the following exercisability would result: (* *
*) of the Warrant Share would irrevocably be exercisable during Year (* * *)
because (* * *) of purchases had been made by the date; the Warrant Shares would
continue to be eligible to be exercisable through Year (* * *) even though an
additional (* * *) had not been purchased, because the average of Years (* * *)
through (* * *) is (* * *); no Warrant Shares would be exercisable in Year (* *
*) even though the

                                      -4-
<PAGE>

NOTE: REDACTED PORTIONS HAVE BEEN MARKED WITH (***). THE REDACTED PORTIONS ARE
SUBJECT TO A REQUEST FOR CONFIDENTIAL TREATMENT THAT HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION.

average purchases of Years (* * *) through (* * *) is (* * *) because an
additional (* * *) of purchases would not have been made by such date; however,
the Warrant Shares should still be eligible to be exercisable at a later date;
(* * *) would be exercisable during Year (* * *) (because the average of Years
(* * *) through (* * *) is (* * *) and because a total of (* * *) of purchases
would have been made); and (* * *) would be exercisable during Year (* * *)
because the average of Years (* * *) through (* * *) is (* * *) and because a
total of (* * *) of purchases would have been made). However, if Dynegy (and its
Authorized Purchasers) purchased (* * *) in Year (* * *) of this example rather
than (* * *), the Warrant Shares would cease being exercisable at the end of
Year (* * *) because the average purchases during years (* * *) through (* * *)
would be (* * *) and only (* * *) of purchases would have been by such date; the
(* * *) became exercisable during Year (* * *) would be unaffected.

          Example 2: If Dynegy (and its Authorized Purchasers) purchases
products and services in anniversary years (* * *) through (* * *) equal to (* *
*), (* * *), (* * *), (* * *) and (* * *), respectively the following
exercisability schedule would result: No Warrant Shares would be exercisable in
Year (* * *) (because purchases were less than (* * *)); (* * *) would be
exercisable in Years (* * *) (because the average for Years (* * *) and (* * *)
is (* * *) and a total of (* * *) in purchases would have been made); (* * *)
would be exercisable in Year (* * *) (because less than an additional (* * *) in
purchases were made after the last exercisability of Warrant Shares and the
average of Years (* * *) through (* * *) is (* * *); (* * *) would be
exercisable in Year (* * *) (because the average for Years (* * *) though (* *
*) is (* * *) and an aggregate of (* * *) in purchases would have been made ((*
* *) - (* * *) = (* * *))); and (* * *) would be exercisable in Year (* * *)
(because the average for Years (* * *) through (* * *) is (* * *) and an
aggregate of (* * *) in purchases would have been made).

          Notwithstanding anything to the contrary hereunder, and subject to
prior exercisability, the Warrant  shall be fully exercisable after March 31,
2005 during its term.

                                      -5-
<PAGE>

NOTE: REDACTED PORTIONS HAVE BEEN MARKED WITH (***). THE REDACTED PORTIONS ARE
SUBJECT TO A REQUEST FOR CONFIDENTIAL TREATMENT THAT HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION.

                                                                        ANNEX II
                                                                        --------

                              NOTICE OF EXERCISE

To: TELLIUM, INC.

     (1) The undersigned hereby irrevocably elects to purchase _____ shares of
Common Stock of TELLIUM, INC., pursuant to the terms of the attached Warrant,
and tenders herewith payment of the purchase price for such shares in full.

     (2) In exercising this Warrant, the undersigned hereby confirms and
acknowledges that the shares of Common Stock are being acquired solely for the
account of the undersigned and not as a nominee for any other party, and for
investment, and that the undersigned shall not offer, sell or otherwise dispose
of any such shares of Common Stock except under circumstances that will not
result in a violation of the Securities Act of 1933, as amended, or any state
securities laws.

     (3) Please issue a certificate or certificates representing said shares of
Common Stock, and pay any cash for any fractional share to:

     Name                    Address                 No. Shares
     ----                    -------                 ----------

     (4) Please issue a new Warrant for the unexercised portion of the attached
Warrant in the name of the undersigned and/or, if the undersigned has completed
an Assignment Form in the form of Annex II to this Warrant, in such other names
and amounts as is specified in such Assignment Form.

Dated: _____________________    Holder: ____________________________

                                By: ________________________________
                                       Name:
                                       Title:

                                      -6-<PAGE>

Note: Redacted portions have been marked with (***). The redacted portions are
subject to a request for confidential treatment that has been filed with the
Securities And Exchange Commission.

                                                                   EXHIBIT 10.27

                              DYNEGY CONNECT, L.P.
                       2821 South Parker Road, Suite 700
                             Aurora, Colorado 80014

                                November 6, 2000

Tellium, Inc.
2 Crescent Place
P.O. Box 901
Oceanport, NJ 07757-0901
Attn: Mr. Nick DeVito, Vice President

     Re:  First Amendment to Purchase Agreement, made as of September 21, 1999
          ("Purchase Agreement"), by and between Dynegy Connect, LP, a Delaware
            ------------------
          limited parnership ("Dynegy Connect") (as indirect successor to
          Extant, Inc.) and Tellium, Inc. ("Tellium")
                                            -------

Dear Mr. DeVito:

     Reference is made to the Purchase Agreement. All capitalized terms that are
     used herein but not defined shall have the meaning ascribed to them in the
     Purchase Agreement.

     This amendment (the "Amendment") to the Purchase Agreement is effective as
                          ---------
     of the date above written.

     For good and valuable consideration, the receipt and sufficiency of which
     is hereby acknowledged, and intending to be legally bound hereby, the
     parties agree as follows:

     The Purchase Agreement is hereby amended as follows:

     1.  Section 1 shall be deleted in its entirety and replaced with the
         following:

          (a) Scope: Subject to the terms, provisions and conditions hereinafter
          set forth, during the term of this Agreement, Dynegy Connect, L.P. and
          the other Authorized Purchasers (as defined in Section 1(b) below),
          including but not limited to European Affiliates of Dynegy Inc., agree
          to purchase, and Tellium agrees to sell, deliver and, if agreed to by
          the parties, install their full optical switch requirements during the
          three (3) year period ending November 1, 2003, including hardware and
          software ("Products") at the prices set forth on Schedule C attached
                                                           ----------
          hereto; provided, however, any commitment to purchase Products shall
          be subject to the Products meeting, in the Authorized Purchaser's
          reasonable discretion, performance standards and current technology
          being deployed at any time during the term of this Agreement. Subject
          to the foregoing, it is expected that Dynegy Connect shall
<PAGE>

Note: Redacted portions have been marked with (***). The redacted portions are
subject to a request for confidential treatment that has been filed with the
Securities And Exchange Commission.

          purchase approximately Two Hundred and Fifty Million Dollars
          ($250,000,000) of Products and installation services described in the
          Schedules, attached hereto and made a part of this Agreement from
          Tellium during the term of this Agreement. It is the intention of the
          parties that Products shall be delivered in such quantities and at
          such times as is set forth in Schedule A attached hereto.
                                        -----------

          (b)  Definitions: For purposes of this Agreement, the following terms
          shall have the following meanings:

                     (1) "Affiliate" shall mean with respect to a person, any
                     other person directly or indirectly controlling, controlled
                     or under common control with such person. For purposes of
                     this definition, "control" when used with respect to any
                     person means the power to direct the management and
                     policies of such person, directly or indirectly, whether
                     through the ownership of voting securities, by contract, or
                     otherwise; and the terms "controlling" and "controlled"
                     have meanings correlative to the foregoing.

                     (2)  "Authorized Purchaser" shall mean

                            (a) DCP Leasing, L.L.C., Dynegy Connect, L.P. or
                            Dynegy Global Communications, Inc. (collectively
                            referred to herein as the "Dynegy Entities");
                                                       ---------------

                            (b)  (***);

                            (c)  (***); and/or

                            (d)  (***).

     2.  The first paragraph of Section 3 shall be deleted in its entirety and
replaced with the following:

          Dynegy Connect will issue purchase orders ("Orders") to Tellium for
       delivery and installation of Products, which Orders will be based on the
       Forecasts (as defined below) delivered pursuant to Section 3.1.

          Other Authorized Purchasers may issue purchase orders to Tellium under
       the Purchase Agreement provided that (i) such Authorized Purchasers agree
       to be bound all applicable terms and conditions of the Purchase Agreement
       insofar, but only insofar, as they relate to the purchase orders issued
       by such Authorized Purchaser and the equipment delivered pursuant to such
       purchase orders, which applicable terms and conditions shall include,
       without limitation, those set forth in this Section 3 and Sections
       4, 5, 6, 8, 10, 14, 16, 23, 29 and 30, and (ii) if the Authorized
       Purchaser for a purchase order is any person other than (***), Dynegy
       Connect or Dynegy Global

                                      -2-
<PAGE>

Note: Redacted portions have been marked with (***). The redacted portions are
subject to a request for confidential treatment that has been filed with the
Securities And Exchange Commission.

       Communications, Inc. then such Authorized Purchaser shall meet the
       reasonable credit criteria employed by Tellium.

           Tellium shall provide Dynegy Connect or such other Authorized
       Purchaser with notice of acceptance of such Order within seven (7) days
       of receipt of the Order. Every Order shall contain a description of the
       Products ordered, the quantities and prices, the delivery date(s), and
       the place of delivery. All such Orders will be made pursuant and subject
       to this Agreement, whether specifically stated or not. In the event of a
       conflict or variance between the terms and conditions of an Order and the
       terms and conditions of this Agreement, the terms and conditions of this
       Agreement shall govern.

           All purchases made by any Authorized Purchaser will be deemed to be
       purchases made by Dynegy Connect (as successor to Extant) for purposes of
       calculating any volume discounts and for purposes of calculating the
       number of, and the vesting of, the Warrants.

    3. Section 4 shall be deleted in its entirety and replaced with the
       following:

                Tellium shall deliver the Products by the delivery date(s) set
          forth in the applicable Order but in no event shall delivery occur
          after the (* * *) after receipt of the Order unless otherwise agreed
          in writing between the Authorized Purchaser and Tellium. In the event
          that delivery of an Order is not made within the respective time
          period specified in Section 29.2, the Authorized Purchaser shall have
          the right to terminate this Agreement in accordance with Section 29.2.
          The Authorized Purchaser's acceptance of the Products shall be in
          accordance with Section 6 at the destination(s) specified in the
          Order. All deliveries shall be F.O.B. Oceanport, New Jersey. Title and
          risk of loss or damage to the Products shall remain with Tellium until
          delivery of the Product to a common carrier for delivery to the
          Authorized Purchaser. Customer shall pay shipping and insurance
          charges. Loss, damage or destruction subsequent to Delivery of the
          Products shall not relieve the Authorized Purchaser or of its
          obligations to pay for the Products.

     4.   Section 5 shall be deleted in its entirety and replaced with the
following:

                (a)  The pricing for Products shall be as set forth in
             Schedule C attached hereto. The prices set forth in Schedule C
             ----------                                          ----------
             are exclusive of all federal, state or local sales, excise, use,
             value added, import or export or similar taxes, other than taxes
             based upon Tellium's net income or corporate franchise. Tellium may
             invoice Customer for any taxes which Tellium will be required to
             collect or pay.

                (b)  All payments shall be made in U.S. Dollars.

                (c)  Products and installation services shall be invoiced
             separately. Products shall be invoiced within (* * *) of delivery
             and installation services shall be invoiced upon acceptance (as
             defined in Section 6).

                                      -3-
<PAGE>

Note: Redacted portions have been marked with (***). The redacted portions are
subject to a request for confidential treatment that has been filed with the
Securities And Exchange Commission.

                (d)  All invoices shall be due net (* * *) from the date of
            invoice.

                (e)  For any amount due hereunder which remains unpaid after its
            due date, Customer shall pay Tellium a service fee of (* * *) of the
            amount due that remains unpaid.

                (f)  (* * *) shall (* * *) and (* * *) the (* * *) to the
            (* * *) for (* * *) to (* * *) or (* * *).

                (g)  Tellium shall provide Engineer & Furnish (Pre-wired and
            Tested OXC) services as set forth in Schedule C, Table 3 for the
                                                 ----------
            first (* * *).

                (h)  When the Authorized Purchasers have (* * *) for (* * *)
            of (* * *), Tellium (* * *) a (* * *) of (* * *) to (* * *) for
            (* * *) stated in (***).

   5. Section 6 is amended as follows:

                (a) The insertion of an (a) at the very beginning of such
            section.

                (b) Each reference to "(* * *)" in Section 6 shall be replaced
            with "(* * *)."

                (c) The following subsection (b) shall be added to Section 6:

                      (b) Installation Services: Acceptance shall have occurred
                      with respect to installation services on the earlier of
                      (* * *) following installation or the carrying of live
                      traffic on the network.

   6. Section 8 shall be deleted in its entirety and replaced with the
following:

          IMPORT/EXPORT.  Each Authorized Purchaser hereby covenants that no
          commodities or technical data (including computer software) or other
          technology agreed to be sold or otherwise transferred under this
          Agreement will be sold, leased, delivered, transferred or conveyed to
          any person in any country except in strict compliance with all export
          and import laws, regulations, executive orders or decrees of the
          United States Government or any agencies thereof and the government of
          any other country (or agencies thereof) with jurisdiction over such
          transaction. Each Authorized Purchaser shall, solely at its own
          expense, obtain all required export and import licenses, permits,
          approvals, certificates and verifications before shipment of any
          Products.

   7. A new paragraph shall be added to Section 16 which shall read as follows:

          Notwithstanding any other provision of the Purchase Agreement, Tellium
          may (i) disclose the terms of this Amendment in any filing with the
          Securities and

                                      -4-
<PAGE>

Note: Redacted portions have been marked with (***). The redacted portions are
subject to a request for confidential treatment that has been filed with the
Securities And Exchange Commission.

          Exchange Commission and (ii) file this Amendment with the Securities
          and Exchange Commission, provided that it uses (* * *) to seek
          confidential treatment with respect to the filing referred to in
          Clause (ii) of this Section 7.

     8. Section 29.2 (c) shall be deleted in its entirety.

     This Letter Agreement may be executed in two or more counterparts, and it
shall not be necessary that the signatures of all parties hereto be contained on
any one counterpart hereof; each counterpart shall be deemed an original, but
all of which together shall constitute one and the same instrument. Delivery of
an executed signature page of this Letter Agreement by facsimile transmission
shall be effective as delivery of a manually-executed counterpart hereof.

             [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                      -5-
<PAGE>

Note: Redacted portions have been marked with(***). The redacted portions are
subject to a request for confidential treatment that has been filed with the
Securities and Exchange Commission.

  Please execute below to evidence your agreement to the foregoing.

                                              Very truly yours,

                                              DYNEGY CONNECT, L.P.

                                              By:   /s/ Michael S. Sava
                                                 --------------------------
                                              Name:  Michael S. Sava
                                              Title: Executive Vice President

ACCEPTED AND AGREED TO:

TELLIUM, INC.

By: /s/ Nicholas DeVito
   ---------------------------------
Name:  Nicholas DeVito
     -------------------------------
Title: VP Business Development
      ------------------------------

DCP LEASING,L.L.C., as Construction Agent for
Polaris Connect Statutory Trust

By:   /s/ Michael S. Sava
    --------------------------
Name:  Michael S. Sava
      ------------------------
Title: Executive Vice President
       ------------------------

DYNEGY GLOBAL COMMUNICATIONS, INC.

By:   /s/ Michael G. Gray
    --------------------------
Name:  Michael G. Gray
      ------------------------
Title: Vice President
       ------------------------

                                      -6-

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