Update: This appears to be a bug which claims you're running Lumia Denim when you're really not. Has anyone encountered this issue too? You can read the original story below.
While I was messing with my phones tonight I got an alert from "Extras and Info", and sure enough, the phones were updated to Lumia Denim. I had just reset both phones, as I've gone back to using my (somewhat beat up) Lumia 1020 as my daily driver after trying out the 635 for a few weeks, so that could have triggered the update. Anyway, both phones are on AT&T plans here in the US, and they're both now running Lumia Denim.
Microsoft announced last week that the Lumia Denim update, which brings Cortana, live folders, and more to Lumia phones, would be rolling out to Windows Phone users soon, but "rolling out" has come to mean anything from "tomorrow" to "in six months", so we're glad to have seen the alert pop up.
Of course I've been on the Developer Preview program since it started, so the phones are fast friends with Cortana already, and I've come to rely on Live Folders to keep me up to date on the numerous email accounts I monitor, but still it's nice to know that the phones are up to date, just in time to have to start over with Windows Mobile 10 as soon as it's available. We'll learn more about that tomorrow.
For now, though, have you been updated to Lumia Denim?