A few months ago, Twitter had introduced new profiles with a header photo. Three months after that announcement, Twitter declared on its blog post that the whole Twitter community will have the new profile by default.
Twitter is rolling out redesigned profile to all the users on December 12. Users don't really have a choice.
The blog post read
If you don't upload a header photo by then, you (and everyone else) will only see a default grey image on your page.
All the users will be able to update their Twitter profiles with a large header image across the top of the page with a smaller profile image in the centre.
Here's a look at a video from Twitter explaining the changes:
Featured Image: credo_vsegd