Want to experience Android 5.1 on your Galaxy S3 today? Even newer smartphones like Galaxy S6 and HTC One M9 don’t have Android 5.1 yet but you can already get it for your Galaxy S3 through CM12.1 ROM.
The CM12.1 ROM builds are available for all AT&T, T-Mobile, Sprint, Verizon, Canadian, and GT-i9300 Galaxy S3 models. Although these are unofficial builds compiled from CyanogenMod sources, they are actually pretty stable, I haven’t found a single bug yet so far.
Since the update from Android 5.0.2 to 5.1 wasn’t a complete overhaul of the OS, we suspect that has a lot to do with its stability as developers don’t have to start from scratch to make everything integrated/stable.