The news come from MuscleNerd himself. The famous jailbreak developer sent out the following from his Twitter account:
Well, the new Redsn0w will only download the essential bits and pieces required for the jailbreaking an iOS device. These “bits and pieces” will be downloaded automatically from Apple’s servers and Redsn0w then applies the jailbreak. The tool automatically finds out which iOS device and which iOS version number is being run and it then applies tethered or untethered jailbreak depending on which kind of jailbreak your device supports.
From MuscleNerd himself:
This auto-downloading and auto-selection of IPSW files is not for beta versions of iOS, so this will not work any of the iOS 5 betas. Instead, you will have to provide the IPSW file yourself. Once it has been selected from Redsn0w, it will be cached so you won’t have to download/select it again.