Apple has begun distributing second betas of OS X Yosemite, iOS 8, Xcode 6, and updated Apple TV firmware to developers. Relatively few details are available so far. The Yosemite beta is listed
simply as build 14A261i, and in release notes for the iOS 8 code, Apple states only that it "contains bug fixes and improvements."
The company is typically quiet about identifying beta changes, often until software is on the verge of public release. Developers however are likely to pick up on any feature additions, which tend to snowball as newer betas are seeded.
The first betas of all four products were introduced earlier this month at WWDC. Apple hasn't set final launch dates for them beyond a broad "fall" window.