The K4 also got a new firmware update and which does indeed work on the gray shelled K4 which was released last fall. The update adds new font support as well as faster page turns. Amazon is also listing KF8 support as a new feature, but the K4 got that in the June update.
This is reassuring; after finding out that there was a new black Kindle 4 I wasn't completely sure if that was a new device or not. Thanks to the update Amazon posted I would say apparently not.
So has anyone tried it? I'm still in the process of charging my K4 so I can install the update, so I don't have any first hand information. What do you think?
Oh, and you can get it here: