The new update is still based on Android 4.1.2 Jelly Bean
Although its dual-SIM counterpart has already been updated to Android 4.2.2 Jelly Bean, the Xperia M single SIM is still stuck on Android 4.1.2.However, there's hope that Sony will eventually offer the long-awaited upgrade in the coming months. As expected, neither version of Xperia M has been included in the initial wave of Xperia smartphones that will receive the Android 4.3 Jelly Bean update.
All in all, XperiaBlog reports that there's a new firmware update 15.1.C.2.8 rolling out now for Sony Xperia M. Sadly, this is still based on Android 4.1.2 Jelly Bean platform, so don't get your hopes high yet.
There aren't any details on the changes, as the update has been deployed without an official changelog attached to it.
Still, we expect it to bring some improvements and bug fixes, so please let us know in the comments if you've noticed any changes since updating to this firmware version.