Earlier this morning, the Lumia Denim update began rolling out in China for numerous Lumia phones. A bit later, Microsoft published a video detailing the how to get the update on their YouTube channel (it was posted earlier on their support site). Now, Windows Central is receiving reports from users that Lumia Denim is rolling out on a broader scale.
Unfortunately, Microsoft has not made an official announcement about the update, unlike Nokia in the past. Likewise, the official update page does not yet reflect the Lumia Denim update, making verification a problem. The third issue is there is a bug with Extras + Info that causes false-positives for the Lumia Denim update. All three are making this job of verifying the true Lumia Denim update slightly challenging.