Surface Pro 3, available to buy today, wasn't the hardware we initially expected Microsoft to announce. What we expected was the Surface Mini, an 8-inch, pen-equipped ARM device that was mysteriously cancelled or delayed at the last minute.
Microsoft appears to have accidentally confirmed that the Surface Mini was indeed planned and all but ready for release with the release of its User Guide for the Surface Pro 3. The PDF is meant to introduce users to all the features that Surface Pro 3 has to offer... but in a handful of places it says not "Surface Pro 3" but "Surface Mini." Search and replace apparently missed a few. The oversight was first spotted by Paul Thurrott.
The references in the document confirm that not only does the Surface Mini exist, but also that it will include pen support, as expected.