I believe MS said phones would receive updates for 18 months. That said, it's most likely going to be up to your carrier. Some carriers are notorious for skipping updates or taking quite a long time to roll them out.
This question has been tackled quite a bit here. I would invite you to use the search button first. And I'm not saying that to be mean like some people, but more so to help you get an answer more quickly and more informative than posting yet another topic such as this. If you search first, you might get not only the answer to your question, but lots of other informative information you might not have normally gotten.
However, to answer question, no one knows except Microsoft. It's speculated that the L9x series and above will get it due to the hardware we have, but again, no one really knows at this point. I believe WPCentral covered an article that stated the L5x series and below would *not* be getting it because the hardware couldn't handle it.