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.
Developers can update to the new beta from the Mac App Store or get a redemption code from the link below.
Apple has also seeded the sixth beta of El Capitan to public beta testers.