|Apple is now seeding a fourth beta of iOS 6.1 to developers. Any major changes are so far unknown, beyond a standard Apple claim of "bug fixes and improvements." Typically, Apple introduces minor features or redesigns with each beta of an iOS upgrade. The download beta is available over-the-air through earlier betas of iOS 6.1, or via Apple's iOS developer portal.
Launching in parallel are a new beta of the Apple TV firmware -- based on iOS -- and a new preview of Xcode 4.6. In both cases, the updates are likely just meant to ensure compatibility with the new iOS release.
Apple may be nearing the final version of iOS 6.1. The company rarely typically only puts out a handful of betas before taking an update public, and may be particularly eager to get v6.1 out before staff break for the holidays and an influx of Christmas gifts causes a surge in iPhone, iPod, and iPad ownership.