The deal, stuck with the official title of "Microsoft Office Pre-launch Offer," started Oct. 19 and ends April 30, 2013. Customers who buy a retail copy of Office 2010 for Windows or one of several stand-alone applications within that period can download a free copy of the corresponding version of Office 2013, or in some cases, choose a free one-year subscription to an Office 365 plan.

Although Microsoft has announced Office 2013, provided a preview of the new suite and named prices, it has not set a launch date. Most expect Office 2013, and the Office 365 plans that rely on it, to ship in late January or early February 2013.

The upgrade or Office 365 subscription will be available when Office 2013 debuts.

Microsoft regularly runs such deals for Office. In 2010, it kicked off a "technology guarantee" for buyers of Office 2007, giving them a free upgrade to Office 2010 for several months bracketing the latter's retail launch.

The difference this time is that Microsoft is giving customers options.