Sony has announced that the Sony Xperia Tablet S Android Jelly Bean update will be released at the end of April and the beginning of May, this is for the Xperia Tablet S and not the original Sony Tablet S.
We will be releasing Jelly Bean for the Xperia Tablet end of April 2013 / early May 2013 for the Xperia Tablet. This update will resolve a memory management issue that may cause the Xperia Tablet to shut down from time to time.
Currently we do not have a roadmap to release the Jelly Bean update for the 1st Generation Tablet (Sony Tablet S).
As you can see from the statement, Sony has not given any details on when the update will be released for the original Sony Tablet S, as soon as we get some more information we will let you guys know.
Source Xperia Blog