The first beta of OS X 10.11.1 introduced support for Unicode 8 and new emoji like taco, burrito, cheese wedge, hot dog, middle finger, and unicorn head. The emoji are also included in iOS 9.1, which is also in testing.
Beyond the new emojis and Unicode 8 support, so far there has been no visually noticeable changes made. In Apple’s release notes for the new build, they state that this release offers stability, compatibility, and security improvements.
All public beta testers can download the new beta right from the “Updates” tab in the Mac App Store.