Exhibit 10.43

OPTION EXERCISE EXTENSION AGREEMENT

This Agreement is made and entered into effective as of December 10, 2008 by and
between Rackspace Hosting, Inc. a Delaware corporation (the “Company”), and
Glenn Reinus, an Optionee of the Company (the “Optionee”).

WHEREAS, Optionee has given notice of his retirement from the Company as Senior
Vice President, Worldwide Sales effective as of 11:59 p.m. on December 31, 2008;
and

WHEREAS, as of December 31, 2008 Optionee will be the holder of 1,510,083 vested
stock options (the “1,510,083 Vested Options”) which were issued under stock
option agreements dated February 25, 2003 and December 31, 2005, respectively;
and

WHEREAS the Company’s Compensation Committee (the “Committee”), appointed to
administer the plans under which the 1,510,083 Vested Options were granted, has
determined that it would be to the advantage and in the best interest of the
Company and its stockholders to grant to Optionee an extension of the right to
exercise the 1,510,083 Vested Options as consideration for increased efforts
during the Optionee’s term of office with the Company.

NOW, THEREFORE, the Company and the Optionee agree as follows:

Rackspace agrees that Optionee will have the right to retain the 1,510,083
Vested Options issued pursuant to the Macro Holding, Inc. stock option
agreements dated February 25, 2003 and December 31, 2005, respectively, and
Optionee will have the right to exercise the 1,510,083 Vested Options in
accordance with said stock option agreements until December 31, 2009, and
Optionee’s right to exercise said 1,510,083 Vested Options shall not terminate
as a result of him not being a Service Provider until December 31, 2009. All
other non-vested options issued to Optionee under the December 31, 2005 Macro
Holding, Inc. Stock Option Agreement and the March 2008 Rackspace, Inc. Stock
Option Agreement shall terminate as of the date hereof. The February 25, 2003
and December 31, 2005 stock option agreements are hereby amended to incorporate
the foregoing agreement.

IN WITNESS WHEREOF, this Agreement has been executed and delivered by the
parties hereto.

 

RACKSPACE HOSTING, INC. By:   /s/ Alan Schoenbaum   Alan Schoenbaum   Senior
Vice President and General Counsel

 

/s/ Glenn Reinus Glenn Reinus