Updated models with AMD graphics options expected in early 2017.
Apple Releases First OS X 10.11.2 El Capitan Beta to Public Beta Testers
The new beta is available through the Software Update mechanism in the Mac App Store to those who are enrolled in Apple's beta testing program. Those wishing to join the program can sign up on Apple's beta testing website.
It's not yet known what improvements the latest update to OS X El Capitan will bring, but it's likely to include bug fixes, security enhancements, and performance improvements to address issues discovered since the release of OS X 10.11.1. Apple's release notes for the first developer beta asked testers to focus on Graphics, Wi-Fi, Calendar, USB, Notes, Photos, and Spotlight.