This is a pre-release update to OS X v10.11. If you have OS X v10.11 installed, download this update by clicking Updates in the toolbar of the Mac App Store. If you do not have OS X 10.11 installed, use your download code on the Mac App Store to get started.
Developer Beta System Requirements
The OS X El Capitan Developer Beta supports the following Macs:
• iMac (Mid 2007 or newer)
• MacBook Air (Late 2008 or newer)
• MacBook (Late 2008 Aluminum, or Early 2009 or newer)
• Mac mini (Early 2009 or newer)
• MacBook Pro (Mid/Late 2007 or newer)
• Mac Pro (Early 2008 or newer)
• Xserve (Early 2009)
Developers can get a download code to install El Capitan from the link below. Apple hasn't listed any new features for the fifth beta but if you spot something, let us know in the comments!