<PAGE>

                                                                     EXHIBIT 4.9

     The securities represented by this certificate have not been registered
under the Securities Act of 1933, as amended.  Such securities may not be sold
or transferred in the absence of such registration unless the Company receives
an opinion of counsel reasonably acceptable to it stating that such sale or
transfer is exempt from the registration requirements of such Act.

                             COMMON STOCK WARRANT

                                      OF

                              CAIS INTERNET, INC.

     THIS CERTIFIES THAT, subject to the terms of this Warrant, for value
received, Cooper Hotel Services, Inc. or its successors and permitted assigns
(the "Warrantholder"), is entitled to purchase shares of Common Stock, par value
      -------------
$.01 per share (the "Common Stock"), of CAIS Internet, Inc., a Delaware
                     ------------
corporation (the "Company"), from the Company in such number and at such price
                  -------
as determined in accordance with this Warrant.

     This Warrant is issued in connection with the Master Agreement for Hotel
Internet Service dated as of June 9, 2000, by and between the Company's wholly
owned subsidiary, CAIS, Inc., and Cooper Hotel Services, Inc.

     Upon delivery of this Warrant (with the Notice of Exercise in the form
attached hereto as Exhibit A), together with payment of the Warrant Price (as
defined below) for the shares of Common Stock to be issued, which payment may be
made by converting this Warrant pursuant to Section 5 below ("Warrant
                                                              -------
Conversion"), at the principal office of the Company or at such other office or
----------
agency as the Company may designate by notice in writing to the holder hereof,
the Warrantholder shall be entitled to receive a certificate or certificates for
the shares of Common Stock so purchased.  All shares of Common Stock which may
be issued upon the exercise of this Warrant will, upon issuance, be fully paid
and nonassessable and free from all taxes, liens and charges with respect
thereto.

     This Warrant is subject to the following terms and conditions:

     1. Term of Warrant.  This Warrant may be exercised in whole, but not in
        ---------------
part, at any time on or after the date hereof; provided, however, that this
Warrant shall expire to the extent then unexercised as of 5:00 p.m., Washington,
DC time, on June 9, 2005.

     2. Number of Warrant Shares.  Subject to adjustment from time to time
        ------------------------
pursuant to Section 4 hereof, the Warrantholder may exercise this Warrant with
respect to 10,368 shares of Common Stock (or other securities issuable in the
event of a reclassification, change, merger or consolidation as set forth in
Section 4(a) hereof) (the "Shares"). This Warrant may be exercised only once for
                           ------
all, and only for all, of the Shares. The Company shall not be required to issue
fractions of Shares on the exercise or conversion of this Warrant. If any
fraction of a Share would, except for the provisions of the

                                       1
<PAGE>

immediately preceding sentence, be issuable on the exercise or conversion of
this Warrant, the Company shall purchase such fraction for an amount in cash
equal to the current fair market value of such fraction.

     3. Warrant Price.  The exercise price of this Warrant (the "Warrant Price")
        -------------
shall equal $17.3125 per share, subject to adjustment from time to time pursuant
to Section 4 hereof.

     4. Adjustment of Number of Shares and Warrant Price.  The number and kind
        ------------------------------------------------
of Shares purchasable upon exercise of the Warrant and the Warrant Price shall
be subject to adjustment from time to time in accordance with the following
provisions.

          (a)  Reclassification, Consolidation or Merger.  In case of any
               -----------------------------------------
capital reorganization, reclassification or change of outstanding securities of
the class issuable upon exercise of the Warrant (other than as a result of a
subdivision, split, combination or stock dividend), or in case of any
consolidation or merger of the Company with or into another entity, the Company,
or such successor entity, as the case may be, shall execute new Warrants, with
substantially the same terms as this Warrant, or amend this Warrant, to provide
that the holder of this Warrant shall have the right to exercise such new
Warrant or amended Warrant and procure upon such exercise in lieu of the Common
Stock theretofore issuable upon exercise of this Warrant the kind and amount of
shares of stock, other securities, money and/or property receivable upon such
reorganization, reclassification, change, consolidation or merger by the
Warrantholder if this Warrant had been fully exercised immediately prior to such
event. Any such new Warrant shall provide for adjustments which shall be as
nearly equivalent as may be practicable to the adjustments provided for in this
Section 4. The provisions of this subsection (a) shall similarly apply to
successive reorganizations, reclassifications, changes, consolidations and
mergers.

          (b)  Subdivision or Combination of Shares.  If at any time while this
               ------------------------------------
Warrant remains outstanding and unexpired, the Company shall subdivide, split or
combine its Common Stock (or declare a dividend or make a distribution payable
in shares of Common Stock or other capital stock), the number of Shares into
which the Warrants are exercisable immediately prior to such action shall be
proportionately adjusted so that the holder of any Warrant thereafter exercised
may receive the aggregate number and kind of shares of capital stock of the
Company which the holder would have owned immediately following such action if
such Warrant had been exercised immediately prior to such action and the Warrant
Price shall be proportionately adjusted.

          (c)  Notification.  Notwithstanding any other provision hereof, to the
               ------------
extent permitted by applicable law, the Company shall provide written notice to
the Warrantholder at least ten (10) days prior to the record date or other
effective date for any of the following actions: dividends, mergers,
liquidations, consolidations, reclassifications of stock, sale of substantially
all of the Company's assets or any other similar action for which stockholder
approval is required by Delaware law.

                                       2
<PAGE>

     5. Payment by Warrant Conversion.  The Warrantholder may exercise the
        -----------------------------
purchase right represented by this Warrant with respect to the Shares subject to
this Warrant ("Converted Warrant Shares") and elect to pay for a number of such
               ------------------------
Converted Warrant Shares through Warrant Conversion by specifying such election
in the Notice of Exercise attached hereto as Exhibit A.  In such event, the
Company shall deliver to the Warrantholder (without payment by the Warrantholder
of any Warrant Price or any cash or other consideration) that number of Shares
equal to the quotient obtained by dividing (x) the value of this Warrant (or the
specified portion hereof) on the date of exercise, which value shall be
determined by subtracting (A) the aggregate Warrant Price of the Converted
Warrant Shares immediately prior to the exercise of the Warrant from (B) the
aggregate fair market value of the Converted Warrant Shares issuable upon
exercise of this Warrant (or the specified portion hereof) on the date of
exercise, by (y) the fair market value of one Share on the date of exercise.
For purposes of this Section 5, the fair market value of a Share as of a
particular date shall be the closing price on the trading day immediately prior
to the exercise of the applicable Warrant.

     6. Notices.  Upon any adjustment of the Warrant Price and any increase or
        -------
decrease in the number of Shares purchasable upon the exercise of this Warrant,
then, and in each such case, the Company, within 30 days thereafter, shall give
written notice thereof to the registered holder of this Warrant (the "Notice").
                                                                      ------
The Notice shall be mailed to the address of such holder as shown on the books
of the Company; and shall state the Warrant Price as adjusted and the increased
or decreased number of shares purchasable upon the exercise of this Warrant,
setting forth in reasonable detail the method of calculation of each.  Any
notice pursuant to this Warrant to be given or made by the Warrantholder or the
Company shall be sufficiently given or made if sent by first-class mail, postage
prepaid, or by next day delivery service for personal delivery, addressed (until
another address is provided in writing by the Company or the Warrantholder) as
follows with a copy to the Company's or Warrantholder's legal departments:

CAIS INTERNET, INC.                      [WARRANT HOLDER]
1255 22nd Street, N.W.
Washington, D.C. 20037
Attn: President
                                         Attention:

     7. Transfer and Exchange of the Warrant and Shares.  When this Warrant or
        -----------------------------------------------
Shares are presented to the Company with a request:

               i)   to register their transfer; or

               ii)  to exchange such Warrant for an equal number of Warrants of
        other authorized denominations,

the Company shall register the transfer or make the exchange as requested if the
following requirements are met:

                                       3
<PAGE>

          (x)  the Warrant shall be duly endorsed or accompanied by a written
     instruction of transfer in form satisfactory to the Company, duly executed
     by the Warrantholder thereof or by his attorney-in-fact, duly authorized in
     writing; and

          (y)  in the case of Shares, such request shall be accompanied by the
     following additional information and documents (all of which may be
     submitted by facsimile), as applicable:

               (A)  if such Shares are being transferred (1) to a "qualified
          institutional buyer" (as defined in Rule 144A) in accordance with Rule
          144A or (2) pursuant to an exemption from registration in accordance
          with Rule 144 (and based on an opinion of counsel if the Company so
          requests) or (3) pursuant to an effective registration statement under
          the Securities Act of 1933, as amended (the "Securities Act"), in each
          case a certification to that effect;

               (B)  if such Shares are being transferred pursuant to an
          exemption from registration in accordance with Rule 904 under the
          Securities Act (and based on an opinion of counsel if the Company so
          requests), a certification to that effect; or

               (C)  if such Shares are being transferred in reliance on another
          exemption from the registration requirements of the Securities Act
          (and based on an opinion of counsel if the Company so requests), a
          certification to that effect.

     8. Miscellaneous
        -------------

          (a)  The terms of this Warrant shall be binding upon and shall inure
to the benefit of any successors or permitted assigns of the Company and of the
holder or holders hereof and of the Common Stock issued or issuable upon the
exercise hereof.

          (b)  No Warrantholder, as such, shall be entitled to vote or receive
dividends or be deemed to be a stockholder of the Company for any purpose, nor
shall anything contained in this Warrant be construed (i) to confer upon the
Warrantholder, as such, any rights of a stockholder of the Company, or any right
to vote, give or withhold consent to any corporate action, receive notice of
meetings, receive dividends or subscription rights, or otherwise, or (ii) as
imposing any obligation on the Warrantholder to purchase any securities or any
liability as a stockholder of the Company, whether such obligation or
liabilities are asserted by the Company or its creditors.

          (c)  Receipt of this Warrant by the Warrantholder hereof shall
constitute acceptance of and agreement to the foregoing terms and conditions.

          (d)  The Company will not, by amendment of its certificate of
incorporation or bylaws or through any other action, avoid or seek to avoid the
observance or performance of any of the terms of this Warrant, but will at all
times in good faith assist in the carrying out of all such terms and in the
taking of all actions as

                                       4
<PAGE>

may be necessary or appropriate in order to protect the rights of the
Warrantholder against impairment.

          (e)  Upon receipt of evidence reasonably satisfactory to the Company
of the loss, theft, destruction or mutilation of this Warrant and, in the case
of any such loss, theft or distribution, upon delivery of an indemnity agreement
reasonably satisfactory in form and amount to the Company or, in the case of any
such mutilation, upon surrender and cancellation of such Warrants, the Company
at its expense will execute and deliver, in lieu thereof, a new Warrant of like
date and tenor.

          (f)  Any provision of this Warrant may be amended, waived or modified
upon the written consent of the Company and the Warrantholder.

          (g)  The Company hereby agrees that at all times there shall be
reserved for issuance and/or deliver upon exercise of this Warrant, free from
preemptive rights, such number of authorized but unissued shares of Common Stock
as from time to time shall be required for issuance or delivery upon exercise of
this Warrant. The Company further agrees that it will promptly take all action
as may from time to time be required in order to permit the holder hereof to
exercise this Warrant and the Company duly and effectively to issue shares of
Common Stock hereunder.

          (h)  This Warrant shall be governed by and construed in accordance
with the laws of the State of Delaware without regard to the conflicts of laws
provisions thereof.


                     [This space intentionally left blank]

                                       5
<PAGE>

     IN WITNESS WHEREOF, the Company has caused this Warrant to be signed by its
duly authorized officer.

Dated: ________ __, 2000

                                             CAIS INTERNET, INC.


                                             __________________________
                                             William M. Caldwell, IV

                                             President

                                       6
<PAGE>

EXHIBIT A
---------

                               NOTICE OF EXERCISE
                               ------------------

TO:  CAIS Internet, Inc.

     1.  The undersigned hereby elects to purchase _____ shares of the Common
Stock of CAIS Internet, Inc. pursuant to the terms of the attached Warrant, and
tenders herewith payment of the purchase price for such shares in full, together
with all applicable transfer taxes, if any.

     2.  The undersigned hereby elects to exercise the purchase right with
respect to ________ shares of such Common Stock through Warrant Conversion, as
set forth in Section 5 of the attached Warrant.

     3.  Please issue a certificate or certificates representing such shares of
Common Stock in the name of the undersigned or in such other names as is
specified below:



             ____________________________________
                  (Name)

             ____________________________________


             ____________________________________
                  (Address)


                                     Signature of Warrantholder:


                                     ____________________________________

                                     By:_________________________________

                                     Title:______________________________

                                     Date:_______________________________

                                       7