Apple has released a 3.1 beta for the iPhone SDK. Both the SDK beta and firmware are available for testing and development to paid members of the iPhone developer program. As pre-release software, any details about this new release remain under NDA.
A pre-installation advisory and beta release notes are available as per Apple's usual release strategy. As before, you cannot use the 3.1 SDK to create applications for submitting to the App Store, so if you plan to download it be prepared to create a separate installation directory.
The new release comes just on the heels of the public 3.0 firmware. Its full-dot-number indicates that it contains more than just minor bug fixes (a relatively minor revision would probably be listed as 3.0.1).
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