Beta 1 is just a continuation of the Alpha and will probably last 6 to 9 months. But now Beta 1 backers can officially join the tests.
Tests will be held throughout the week
Alpha backers will have access to all tests (except internal IT testing).
Beta 1 backers will have access to weekend tests and some tests during the week.
Beta 2 backers will occasionally be invited to certain tests.
Game is still bare bones. They have 3 classes for each realm (tank, healer, range dps). They use these in various tests to stress systems, etc. The tests are usually short matches with as many players and bots that they can hold.
The engine is getting pretty stable so now they will start adding various mechanics and systems to the build. Adding complexity and refining the maps in the world, getting ready for Beta 2, etc. Other classes will not be added until much later, probably not in Beta 1.
This is not in any way close to Open Beta. That is still a very long ways off.