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                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                            ------------------------

                                  FORM 10-K/A
                                AMENDMENT NO. 1

                   FOR ANNUAL AND TRANSITION REPORTS PURSUANT
         TO SECTIONS 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

(MARK ONE)

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<C>        <S>
   /X/     ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
           SECURITIES EXCHANGE ACT OF 1934 FOR THE FISCAL YEAR ENDED
           DECEMBER 31, 2000
</Table>

                                       OR

<Table>
<C>        <S>
   / /     TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
           SECURITIES EXCHANGE ACT OF 1934 FOR THE TRANSITION PERIOD
           FROM TO
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                         COMMISSION FILE NUMBER 0-26303

                            ------------------------

                               VIANT CORPORATION

             (Exact Name of Registrant as Specified in Its Charter)

<Table>
<S>                                             <C>
                DELAWARE                              77-0427302
    (State or other Jurisdiction of                (I.R.S. Employer
     Incorporation or Organization)              Identification No.)

      89 SOUTH STREET, BOSTON, MA                       02111
(Address of Principal Executive Offices)              (Zip Code)
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                                 (617) 531-3700
               Registrant's Telephone Number, Including Area Code

        SECURITIES REGISTERED PURSUANT TO SECTION 12(B) OF THE ACT: NONE
          SECURITIES REGISTERED PURSUANT TO SECTION 12(G) OF THE ACT:

                    COMMON STOCK, $.001 PAR VALUE PER SHARE
                                (TITLE OF CLASS)

    Indicate by check mark whether the Registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes /X/  No / /

    Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendments to
this Form 10-K. / /

    The aggregate market value of the voting stock held by non-affiliates of the
Registrant was approximately $77,844,000 on March 29, 2001 as reported by
NASDAQ. Shares of voting stock held by each officer and director and each person
who owns 5% or more of the outstanding voting stock have been excluded in that
such persons may be deemed to be affiliates. This determination of affiliate
status is not necessarily a conclusive determination for other purposes. There
were approximately 50,139,000 shares of Common Stock outstanding as of
March 29, 2001.

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EXPLANATORY NOTE

    On April 2, 2001, Viant Corporation (the "Company") filed its Annual Report
on Form 10-K for the fiscal year ended December 31, 2000 (the "Annual Report"),
with the Securities and Exchange Commission. The purpose of this amendment is to
clarify certain items in the Annual Report.

                                    PART III

ITEM 11.  EXECUTIVE COMPENSATION

    The information required by this Item is incorporated by reference to our
proxy statement.

ITEM 12.  SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT
          PRINCIPAL STOCKHOLDERS

    The information required by this Item is incorporated by reference to our
proxy statement under the heading "Security Ownership."

ITEM 13.  CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

    None.
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                                   SIGNATURES

    Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the Registrant has duly caused this amended Report to be
signed on its behalf by the undersigned, hereunto duly authorized, in Boston,
Massachusetts, on the 22nd day of August 2001.

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<S>                                                    <C>  <C>
                                                       VIANT CORPORATION

                                                       By:              /s/ ROBERT L. GETT
                                                            -----------------------------------------
                                                                          Robert L. Gett
                                                              PRESIDENT AND CHIEF EXECUTIVE OFFICER
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    Pursuant to the requirements of the Securities Act of 1934, this amended
Report has been signed by the following persons in the capacities and on the
dates indicated:

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<Caption>
                   NAME                                      TITLE                        DATE
                   ----                                      -----                        ----
<C>                                         <S>                                      <C>
           /s/ ROBERT L. GETT*
    ---------------------------------       President, Chief Executive Officer and   August 22, 2001
              Robert L. Gett                Director (Principal Executive Officer)

          /s/ M. DWAYNE NESMITH             Vice President and Chief Financial
    ---------------------------------       Officer (Principal Financial and         August 22, 2001
            M. Dwayne Nesmith               Accounting Officer)

          /s/ KEVIN W. ENGLISH*
    ---------------------------------       Director                                 August 22, 2001
             Kevin W. English

         /s/ VENETIA KONTOGOURIS*
    ---------------------------------       Director                                 August 22, 2001
           Venetia Kontogouris

          /s/ WILLIAM E. KELVIE*
    ---------------------------------       Director                                 August 22, 2001
            William E. Kelvie
</Table>

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<S>   <C>
*By:            /s/ M. DWAYNE NESMITH
          ---------------------------------
                  M. Dwayne Nesmith
                   Attorney-in-fact
</Table>

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