I downloaded OS X 10.11 Developer Beta and it shows up in the AppStore Purchases list as "Downloaded", but it never shows up on the Updates page. How can I install El Capitan?
I'll answer my own question, just in case anyone else has the same problem.
The AppStore silently placed an app in my /Applications folder named "Install OS X 10.11 Developer Beta.app", which I double-clicked to run. Seems obvious now, but I didn't know to look for an app in my Applications folder. Previous beta releases just installed themseleves.