Yes, that’s right, a Jelly Bean 4.1.2 firmware was leaked on xda. This just comes a day after Samsung was reportedly starting to work on a Jelly Bean update for the device.
The leaked rom is apparently a test firmware (REV00) which may contain several bugs. A battery drain was already confirmed by xda members and a possible temporary fix was posted. Nevertheless the rom works perfectly without any major issues. The new TouchWiz UI works flawlessly as in a final rom. There are some minor issues especially a little bit of lag and hardware acceleration issues in some games but any inconsistencies shall be fixed later on when Samsung finally releases the final build in few weeks.
So far reported issues are:
– GPU related issues probably due to vsync or hardware acceleration
– Battery Drain, probably a deep sleep issue/wakelock
– TouchWiz UI will sometimes crash & FC
– Lags in Gallery which could be caused by the Android media scanner
– Autofocus issues with the back camera
As usual, installing the rom will require Odin and few other device specific files (which are already included in the leaked file) and a bit of patience, users wanting to proceed at their own risk can find a step by step guide posted here. Download links are just below, the whole archive is around 915Mb and split across 7 parts.