Unlike the also new Pentax Q camera, which achieves super-compactness via a very small sensor though, the Pentax K-01 has a big, APS-C sized one. Interesting, didn't see this coming right now.
Here's another surprise: it's not a new lens mount!
The decision to retain the same lens mount is a bold one, and makes the Pentax K-01 truly unique, as of this writing. Every other compact system camera on the market has a new mount, and a relatively limited selection of optics from which photographers can choose. Most have provided adapters to allow use of historic glass from their earlier SLR cameras, but sometimes with limitations in terms of focusing and exposure that may make their use less attractive. The K-01, by contrast, can be used out-of-the-box with a vast selection of Pentax glass produced over a period of decades, as well as third-party glass for the Pentax K-mount.
So that means that for instance my compact, high-quality portrait Pentax lenses will work with it. Kudos to Pentax for that.
This will surely limit how compact Pentax can make new lenses though, as they haven't shortened the lens-to-sensor distance like everybody else who took out the mirror. We'll see how this goes in practice.
Of course, the camera also is as thick and heavy as the DSLR predecessors, unlike other mirror-free cameras (Micro Four Thirds for example). So apart from eliminating some moving parts and a little noise and vibration, I wonder what is really supposed to be the advantage of this model over Pentax's DSLR models, like the excellent K-r and K-5.
The K-01 also does not have an electronic viewfinder, only the screen on the back.
