Jeez, give Apple a minute to push it to the app. You checked for it moments after it had been released. I don't have any fancy red arrows, but mine shows the update is available when I select "check for updates."
I had be on Yosemite on the iMac and maybe a week (or two) ago the El Capitan OSX update was pushed.... The iTunes update was shown in the list of packaged updates ( as well as updates to Safari and a Security update..... So all were done at once.