If you haven’t signed up for The Elder Scrolls Online beta yet, content in your certainty that there will be an open beta before the game launches, I have the unfortunate task of disillusioning you. There will be no open beta.
From the game’s support FAQ, updated last week:
We will not be holding a traditional open beta, but if you sign up to participate in the ESO beta prior to launch and are eligible per our Terms of Service, you will get an invite to a future beta event. We will be holding several very large beta sessions that include beta key giveaway promotions before the game launches. Please make sure to sign up for beta if you have not yet done so: https://www.elderscrollsonline.com/en/beta
So if you want to get to Tamriel early, get yourself signed up.
The Elder Scrolls Online releases to the PC and Mac on April 4, 2014 and to the Xbox One and PS4 in June of 2014.