The ASUS Transformer Prime is getting its third OTA update in a month today, with reports of a large-scale rollout happening as we speak. This update puts the build number at 18.104.22.168, and is reported to address the widespread random reboot issues folks have been seeing since the last update a few weeks ago. There's likely other changes, but ASUS hasn't released a change log just yet.
What we do know, and this is all based on user reports, is that this update seems to run poorly the first few minutes after a reboot, so give it some time to settle after you apply the OTA. You can check for the update yourself by going into the settings and forcing the check in the About Tablet screen. We'll keep our eyes open for an official change log, and update when it appears. In the meantime, hit the forums and join the discussion!