Snapchat's redesign has really taken off, slimming the app down to two sections: Friends and Discover. Snapchat appears to be celebrating this massive success by giving all users a sort of "best of" filter, one that encapsulates the complete Snapchat experience complete with the Dancing Hot Dog.
This filter (which you access by long-pressing the main screen) has applications for both your front and rear camera. The front camera will offer a filter that puts the Snapchat logo, hearts, and stars on top of your head. The rear camera offers an acid trip of an AR experience, one that takes you through some of Snapchat's greatest inventions. The Dancing Hot Dog is notably front and center.
We reached out to Snapchat for clarification, and this new filter is indeed intended to commemorate the upcoming redesign. We're thrilled that Snapchat has been such a huge success, because we get to keep having fun with it! Congrats, Snapchat on your redesign.