Ratchet & Clank: All 4 One is getting a limited beta test in preparation for the October 18 launch. Codes are currently going out to fans who attended the Insomniac Community Day or won a contest. If you're not in on the beta yet, Insomniac will be giving out more codes through Facebook and Twitter. Amazon will send codes to those who pre-order before September 27.
A beta is especially important for this Ratchet game, because it's one of the few games in the series to feature online play. As the name implies, it focuses on four-player cooperative action.
The PlayStation Blog details the beta. It includes the opening level of Luminopolis, and the Vertigus Cliffs. The first is an introductory stage, but the cliffs let you use the weapon wheel to select a wide variety of the series' signature weapons, along with new ones like the Frost Cannon, Plasma Bomg Launcher, and Warmonger. You can also try out each character's special ability, and play as Ratchet, Clank, Qwark, and Dr. Nefarious.
If you want to try the game but can't make it into the beta, you'll have another opportunity soon. Insomniac is planning an official demo for October.