Back in April, Google began experimenting with a new, alternate version of its Material UI for the Chrome browser - but it was as an experimental flag, not a mainline feature. That appears to be changing. With the latest builds of Chrome on the Canary channel for Windows, Linux, and Chrome OS, the Material 2 UI is now the default theme (on Mac you'll still need to enable it manually).
There are some changes from the version that was initially unveiled - tabs are now separated by small break lines instead of the more subtle rounded rectangle (only the currently open tab is shaped this way in the latest revision). Spacing between the back, forward, and refresh buttons appears to have grown - probably to optimize for touchscreens - and things look a bit less cluttered as a result.
According to François Beaufort, there are also small tweaks to the omnibar, pinned tabs, coloring, and various other areas. You'll have to try it out to really get a sense for all of the differences, but the fact that it's the default theme in Canary pretty much assures that some variation of this will be trickling down to the other channels soon enough. The design language is based on Google's latest iteration of Material Design (informally, Material Design 2), which heavily featured at Google I/O earlier this year.
While Google had been testing another Material interface for Chrome (present on dev and beta channels currently for some platforms), it appears this "alternate" design won out, and I have to say I agree with the decision there. It looks cleaner, more playful, and definitely more modern.
- François Beaufort