A new report is suggesting that Microsoft have already begun rolling out the Office 2013 RTM to Windows RT users. This means that everyone who have purchased a Surface or RT device will get access to the full Office 2013 version on launch day. So no more Office 2013 preview for them!
The update includes bug fixes and removes the "preview" tag from Office all together. The update is 580MB can be downloaded from Windows Update on Windows RT devices.
There has been no word on a release date for RTM on normal Windows 8 installs, but is expected to begin selling Office 2013 sometime in early 2013.