The patch notes for 2.1 have been released, you can read all the information here, and there's quite a bit of it!
Also, as of 2:00 EST / 11:00 PST the download for the patch is available on the client. The patch itself is weighing in at a healthy 3gb. Start as early as possible!
Maintenance is scheduled to end at Midnight PST / 3 AM EST, but may be completed before that time.