The Lenovo ThinkPad X1 Carbon Review (2015) The X1 Carbon has been Lenovo’s flagship ThinkPad since it was launched, and it brings the world of the ThinkPad business class notebook down into a much thinner and lighter form factor. Today we have the third generation of the X1 Carbon, and although the competition for the best Ultrabook keeps increasing, Lenovo brings a lot to the table with the X1 Carbon.