Just like it does with Windows, Microsoft typically offers its Office customers an upgrade guarantee program, allowing them to buy the current version of a product with a free or discounted upgrade to the next one being part of the package.
One of my contacts said the Office 2013 upgrade guarantee will begin in about a month's time -- specifically on October 19. If this is correct, users purchasing Office 2010 between that date and the end of the covered period (which my same contact said is April 30, 2013) will get some kind of guaranteed upgrade to Office 2013 once it is generally available.
Microsoft officials have not shared public guidance as to Office 2013's planned release-to-manufacturing (RTM) or general availability dates. My sources have heard that the RTM target is November 2012, with general availability slated for February 2013. (Those with TechNet/MSDN and volume-licensing agreements would likely get the final bits shortly after they RTM.)
Microsoft offered the Office 2010 tech guarantee program for those purchasing Office 2007 as of March 2010. The period of coverage was seven months, roughly the same amount of time the Office 2013 tech guarantee supposedly will last.
The Office 2010 tech guarantee upgrade program was free. It's unknown whether the Office 2013 one will be, as well. If Office follows Windows' lead, it may not be. Microsoft announced it will be charging those who purchase Windows 7 PCs between June 2 and January 31, 2013, $14.99 to obtain an upgrade to Windows 8 Pro once it is generally available. The Windows Vista upgrade program before this was free.
My contact sent me a couple of screen shots of what allegedly appeared briefly on the Office.com/offer page (which is not currently available), which I have included below.
It appears the upgrade offer for Office will be for Windows users who purchase Office 2010 Home & Student, Home & Business 2010, Professional 2010 or University 2010 and Mac users who purchase University 2011 or Home & Student 2011 between October 19 and April 30, 2013. Windows users who buy these SKUs will have a choice of upgrading to Office 365 Home Premium (which is currently one of the new Office versions that is being beta tested) or Office 2013 SKUs that are more comparable to what's out there already.
The chart above shows some of the differences between Office 365 Home Premium and these more traditional Office 2013 releases. Office 365 Home Premium can be installed on up to five PCs and/or Macs and is licensed to a user as a one-year subscription, which will need to be renewed to continue usage. The more traditional Office 2013 SKUs can be installed on only one Windows PC with a non-transferrable license. (The Office for University and Mac Home & Student users will have the option to upgrade to Office 365 Home Premium only.)
I am not sure whether these Office upgrades will be free, but given there's no visible price on these screen shots, I'd say there's a chance.
I've asked Microsoft for comment on the details and dates of the coming Office upgrade program but have yet to hear back.
Update: Microsoft officials said they had no comment on anything about the alleged Office upgrade program.
Update (September 17): Microsoft officials confirmed all the details about the upgrade offer in my original post were correct, including the start and end dates and the SKU listings. The listed upgrades will be free to users who purchase Office 2010 between October 19 and the end of April, officials said.