There's some confusion out there with regards to the 64-bit client, and while there's not an official blue post today about it, there is a fair amount of information from previous blue posts from which we can put together a pretty accurate picture.
If you don't know what a 64-bit client is or have no idea in general what I'm talking about, Mat McCurley wrote a good piece on what this is all about earlier in the month.
So the 64-bit client wasn't contained in the patch you all just downloaded; it's still in beta. The client that's available to download from the PTR forums right now doesn't work with the live and patched servers -- it throws the "Unable to validate game version" error. We're unsure exactly if Blizzard will be releasing a beta 64-bit client to use on the live realms today, but we've reached out to ask and will update if and when we hear back.