Apparently Shuttleworth announced at the OpenStack Summit that Ubuntu 18.04 will have ten years of support (originally cited ZDnet article). But neither the Ubuntu website nor the Ubuntu wiki have been updated to reflect that.
What exactly is included in this ten-year support?
I'm not looking for speculation or guesses or indications. I'm looking for verifiable, official information.
The Releases page has some clear dates for how long security support will last.
For 18.04, it's 5 years of standard security support + 5 years of ESM (ESM = "Extended Security Maintenance").
We (Canonical) do need to improve on publishing the ESM source package list more in advance.
From either list on the Releases page you can see what packages were included in previous releases to get a general idea. Desktop packages are not being considered.
I'll update this answer as we publish more.