Both systems will be running Ubuntu 14.04 SP1. This is the long-term support (LTS) version of Ubuntu. It will be supported by Ubuntu's parent company Canonical for five years after its release: April 2019.
According to Barton George, Dell's Director of Developer Programs, in a blog posting, programmers had been asking for a bigger, better officially supported Ubuntu Linux developer laptop and that's the Precision M3800 . This came about from a combination of the efforts of Dell software engineer Jared Dominguez and enthusiastic user support.
Sound good to you? To get the M3800 developer edition, go to the Dell Precision M3800 Mobile Workstation page and choose the system labeled "Fully Customizable" on the far left. The next Ubuntu-powered XPS 13 isn't available yet, when it is, it will list for approximately $50 less than the corresponding windows configuration.