Geek Technica

Officially Chrome OS is following the same versioning trend as Chrome browser. The tarball packed chromium source that was initially released for everyone to build Chrome OS from scratch was 0.4.22.8 and the dev channel (nightly builds) Chrome browser is 4.0.249.11 (as of this writing). But Chrome OS user-string reveals a bit more about the current OS version. I am sure you can get the same information by checking out the source but this is a less time consuming way to find out.

Chrome Browser dev channel user-agent string under Windows 7:

Operating System:    Macintosh WinNT

Browser:             Safari 1.3

                     Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US) AppleWebKit/532.5 

                     (KHTML, like Gecko) Chrome/4.0.249.11 Safari/532.5

Chrome OS user-agent string:

Operating System:    Macintosh UNIX

Browser:             Safari 1.3

                     Mozilla/5.0 (X11; U; CrOS i686 9.10.0; en-US) AppleWebKit/532.5 

                     (KHTML, like Gecko) Chrome/4.0.253.0 Safari/532.5

Even though the Chrome browser running on Chrome OS seems to be dev builds of the browser, the underlying OS identifies itself as CrOS i686 9.10.0, or more specifically version 9.10. This might have something to do with the fact that Ubuntu developers have been privately working with Google on Chrome OS way before it was officially announced in July 2009.

Taking these information into consideration I think it is safe to conclude that, under the hood, Chrome OS is nothing more than a stripped and dumbed down version of Ubuntu 9.10 Karmic koala with Chrome browser acting as a light-weight desktop environment (similar to XFCE or xubuntu).