Earlier this week, Microsoft announced that the Nokia Lumia Icon would soon be eligible for Insider Preview builds from the Redstone Development Branch. Today is the day that it becomes a reality.
The build that you can get from the Fast ring is the latest, 14332. No matter what you're upgrading from, it contains a ton of new features.
The Lumia Icon now holds the honor of being the only device that's eligible for Anniversary Update previews, but which isn't eligible for an "official" upgrade.
As always, it's worth noting that even though you can't get that "official" upgrade, there's very little difference between the Release Preview ring of the Insider Preview and upgrading through Upgrade Advisor. There is no device-specific firmware that comes with an official upgrade, so the only difference is that with the Release Preview ring, you get cumulative updates a little earlier than everyone else.