This is the latest model XO laptop, and it was announced earlier this year. This model adds an IR touchscreen, HDMI port, and faster dual-core CPU, but otherwise looks identical to the original XO-1. It's expected to ship with either 1GB or 2GB of RAM and 4GB or 8GB of storage. Prototype units were shipped to a limited number of testers a couple months ago, and one was kind enough to show the XO-4 was capable of displaying Kindle ebooks:
That was a fun device to play with, but it still felt not quite finished. It was also fun to correct the Marvell rep who was demoing it. (I knew more about it than he did.) On a related note, I was told that OLPC will be making some announcement about it this week. I could not get any details from Marvell on whether any units had been ordered, or when they would leave the factory, but I suspect that is what OLPC is going to talk about.
Update: OLPC is now saying that the XO-4 will cost $206 when ordered in quantities of 20,000. It's expected to start mass production in March of this year.