Update: The actual OS version of this update is 10.0.9.2320. The number in the article title v10.9.9.339 is actually the bundle version number that the OTA update shows.
Well, this was unexpected! Looks like RIM has pushed out another update to the BlackBerry 10 Dev Alpha device. As I'm currently downloading the v10.9.9.339 update to my Dev Alpha, I can't help but wonder what it will contain? More features? Perhaps this will be the fail/safe update that kills the Dev Alpha at a specific date to make sure no one else sells them online.
Go to your Settings... Software Update... and select 'Check For Updates' to begin downloading your new update. Be sure to let us know of anything new you may find. Mine's just about done installing. So I'll be reporting more on the update soon.