today sony have announced via Twitter that PlayStation 3 System Software version 4.21 is incoming with details below.
Download: PS3 Firmware 4.21 Update (US) / PS3 Firmware 4.21 Update (EU)
Currently it is an optional (non-mandatory) PS3 update, and below is what Sony stated in their Tweet on the revision, to quote:
"PS3 system software update 4.21 will be released soon. It's a minor, optional update that improves software stability."
As always, we will update this post as more details are available!