People who are currently participating in the Arma 3 Alpha will gain access to the Arma 3 Beta through an automatic Steam update
Bohemia Interactive sent over a press release announcing that ArmA III, a brand new installment in its series of realistic military simulators, will enter beta testing on June 25th. The Arma 3 Beta features a varied selection of brand new content - including 10 vehicles, 7 weapons, 4 showcase missions (Combined Arms, Supports, Commanding & Night), 2 multiplayer scenarios and 4 challenges.
The price of the Arma 3 Beta, in comparison to the Arma 3 Alpha, will be increased. The regular Arma 3 Beta will be available for 34.99 EUR/29.99 GBP/44.99 USD (current price: 24.99 EUR/19.99 GBP/32.99 USD), while the Arma 3 Digital Deluxe Edition will be sold for 44.99 EUR/39.99 GBP/59.99 USD (current price: 39.99 EUR/34.99 GBP/49.99 USD). Note that the current (heavily discounted) Alpha deal, which includes Beta-access and the full game, will still be available until Tuesday June 25th.