Apparently Microsoft will be shipping a Preview version of Office 2013 RT as part of its Windows RT ARM-based tablets later this year. That version will apparently be upgradeable to a final copy in early 2013.
This is all subject to any official confirmation from Microsoft.
(http://i47.tinypic.com/s5acmb.jpg)
Microsoft is planning to remove certain features from its Office 2013 RT edition, according to sources familiar with the company's plans. The software maker is planning to ship a Preview version of Office 2013 RT as part of its Windows RT ARM-based tablets later this year. We understand the Preview edition will be upgradeable to a final copy that will be made available in early 2013.
To optimize for Windows RT, Microsoft has made the decision to remove a number of features from its Office 2013 RT release to ensure battery life and reliability are not impacted on tablet devices. Macros, third-party add-ins, and VBA support will all be dropped from the Office 2013 RT edition, and one source says a "small number" of other features have also been removed. We'll have to wait for Microsoft to detail all of its changes, but although a spokesperson says the company has "not finalized any packaging," we understand that Microsoft Office Home & Student 2013 RT Preview will come preinstalled on all Windows RT devices.