Lumia Denim starts to roll out today to selected Lumia models in China
Other changes include the latest update to the Lumia Camera app, which helps the camera boot up faster than before. It also allows you to snap a series of pictures with just a fraction of a second between shots. And on some models, Moment Capture will allow you to record video in 4K and capture HD photos from the video. The update also allows you to add either Bing Weather or Bing Health and Fitness data to the Glance screen.
Since the update is being sent out on a staggered basis, don't feel bad if it doesn't hit your phone today. It might take a few days before everyone receives it. And you can also try to manually pull Lumia Denim out of your phone by going to Settings > Phone update > Check for updates.
source: MicrosoftChina (translated) via WindowsCentral