A 75 GB update for the Diablo 4 client became available earlier today, suggesting Closed Beta may start soon.
Diablo 4 entered very limited testing almost a month ago when select players were invited to partake in a confidential test. The client has now been updated with a new 75 GB update which is available for download. Check your Battle.net client and e-mail. Beta may just be around the corner!
More details about the patch can be found on BlizzTrack.