Initially slated for launch in Dec 2015 HTC delayed the release of their VIVE virtual reality headset due to a supposed breakthrough in it's development. This breakthrough has been revealed as a front facing camera and an upgrade to their chaperon system that helps VIVE users stay within the bounds of their play space and prevents bumping into obstacles or hitting surrounding walls.
This upgrade allows users to double tap a button on the VIVE controller to seamlessly switch between the virtual world and a stylized view of their actual surroundings as seen by the new front facing camera. When switching views the outside world is shown with a matrix like overlay, this overlay allows users to easily identify their surrounding while reducing the jarring affects of rapidly switching between VR and real-life. As well as the ability to switch views the chaperone system which previously showed a grid like barrier when approaching nearby walls will now show the users actual surroundings with the same matrix-esque overlay.
Due to this upgrade HTC have developed a second VIVE development kit the VIVE PRE which includes the new front facing camera as well as improved ergonomics and upgraded lenses. Along with the upgrades to the HMD itself HTC have upgraded the VIVE controllers with improvements in ergonomics and battery life which was one of the the major gripes heard from developers using their Dk1 controllers.
HTC are planning to ship over 7000 of these VIVE Dk2's to developers to help integrate these new features into their projects. Although shipping of the VIVE PRE to developers has only just begun HTC have announced that pre-orders for the final consumer version of the VIVE will start on February 29th with shipping set to start in April. How much of a difference there will be between the specs of the VIVE PRE and the final consumer product is still unknown but I suspect they will be very similar.
Pre-order costs are still unknown but if HTC can keep the costs close to that of the Oculus Rift ($599 USD) I expect that many will be cancelling their Rift and jumping ship to HTC.