3DMark also features a new UI that's faster and more flexible. The new Home screen shows the recommended benchmark for your system. You can install and run other tests from the Benchmarks screen.
Futuremark has also rebuilt the internals of the 3DMark app. You can now download, install and update benchmarks independently. This makes the initial download much smaller. And it means you can choose to install only the tests you need.
The beta is open to everyone who owns the Steam version of 3DMark.
If you have the standalone version, and you don't want to wait for the update in 2016, this FAQ explains how to add your 3DMark key to Steam.
To join the beta, follow the steps in Futuremark's community post on Steam.