The beta kicks off on Saturday, December 9, at 9 AM PT / 12 PM ET / 5 PM GMT and runs through the same times on Tuesday, December 12. You'll need to have 5.9 GB of space available on your console to download it and be a PS Plus member to participate. You can download the beta here.
The beta features 14 different weapon types to use, as well as three different quests across two environments: the Ancient Forest and Wildspire Waste. The former is home to the Great Jagras and the Anjanath, while the rock-headed Barroth can be found in the latter. Each quest can be completed either solo or with up to three other players; if you manage to clear all three before the beta ends, Capcom says you'll earn "some useful bonus items" in the full title.
Source: GameSpot