Asus has confirmed that an Android 4.1 Jelly Bean update is coming to most of its Transformer-series tablets.
Asus sent out a press release stating that an Android 4.1 Jelly Bean update is coming to the "ASUS Transformer Pad, ASUS Transformer Pad Prime and ASUS Transformer Pad Infinity" over the "coming months". We're taking the "Transformer Pad" to mean the Pad 300, aka the TF300, rather than the original Transformer tablet.
However, the release says that Asus is "still investigating" a Jelly Bean update for devices like the first Transformer - don't lose all hope yet. There is a small possibility that the tablet does not meet the minimum specs of the new Android OS, but this seems unlikely when the software isn't intended to be exclusive, and the original Transformer isn't yet 18 months old. Rather, it seems more likely that the first tablet has simply slipped down the priority list.
Asus writes that it'll be back with more specific release date info in due course.