New ~10.5-inch model with nearly bezel-free design rumored.
Apple Seeds Third Beta of macOS Sierra 10.12.5 to Developers and Public Beta Testers
The third beta of macOS Sierra 10.12.5 can be downloaded through the Apple Developer Center or through the Software Update mechanism in the Mac App Store.
According to the release notes accompanying the beta, the update "improves the stability, compatibility, and security of your Mac."
Apple's release notes don't often provide a lot of insight into what's included in new beta software, so we don't know what features or bug fixes might be included in the 10.12.5 update.
No notable changes or major bug fixes were discovered in the first two betas, but should anything pop up in the third macOS Sierra 10.12.5 beta, we'll update this post.
Update: Beta 3 is also out for public beta testers.