After the launch iOS beta 6 4 MuscleNerd stated that version 0.9.13 dev 3 a redsn0w still jailbreak iOS 6 beta 4, though to jailbreak an ipsw al must be used iOS beta 6 3. Unfortunately, this beta version does not install the application Cydia because the Dev Team does not consider that developers need the automatic installation of this application, however using this tutorial you can install it too. Those who installed Cydia on iOS 6 beta 3 stated that the Cydia application is not functional and I don't see why the problem would resolve itself in iOS 6 beta 4, so be prepared for the same result.
You can download redsn0w 0.9.13 dev 3 available here.
