Keeping true to its promise, Apple today launched the OS X 10.11 El Capitan software update for the Mac. El Capitan has the same system requirements as Yosemite, meaning it should run on any Mac introduced in 2009 and later, and some models introduced in 2007 and 2008.
The software update offers several new headline features while packing in a bunch of under-the-hood refinements designed to make your Mac run faster and more efficiently than before.
If you don't see the update in the Mac App Store's Updates tab yet, give it a while as these things take time to propagate through the Interwebs. By the way, you can manually run a search for 'El Capitan' in the Mac App Store and install it from there.