As outlined on EA's website, the test will be quite brief-it'll run from December 8-9, though it'll be available on all three of the game's platforms: PS4, Xbox One, and PC.
The alpha will be available for PC, PlayStation 4, and Xbox One.
The Anthem alpha will be taking place in a series of closed sessions on the two days in question. EA has acknowledged that matchmaking and server load will be adjusted "on the fly", and that the alpha will be "limited" in what it shares. EA and BioWare are offering a limited Closed Alpha test that will run the weekend of December 8-9. Signing up does not guarantee entry into the alpha as it is on a "first come first served" basis.
You can register for the test here.
The signing process asks you to agree to a NDA so you won't be able to discuss the game and its content openly without EA's approval. You can play in one or all of the tests. "Once the Community Playtest has started, check your email to see if we've sent you instructions to download the Anthem Closed Alpha client".
The Closed Alpha isn't tied to pre-orders or EA Access/Origin Access membership.
Anthem, which is scheduled to launch on February 22nd next year, has struggled to win over fans skeptical of game's dramatic departure from BioWare's usual story-rich, single-player fare. Full details can be found on the publisher's Anthem Closed Alpha page. Once your application is accepted, you will get notified. Once you are registered and signed in, choose the platform of your choice and submit. We've already signed up ourselves, and will keep you updated if BioWare and EA decide to open up the Closed Alpha to even more players in future.