Source: Alessandro Paluzzi
Twitter has confirmed it's trying a new feature to let two accounts co-author one tweet. App researcher Alessandro Paluzzi has posted evidence of this feature since at least December. But recent development shows an official-looking dialogue box from Twitter about how the feature works. The concept is similar to what Instagram launched last year. Attaching two users two a tweet can be helpful for things like brand partnerships, influencer campaigns, or just sharing credit for a funny post.
Based on the leaked screenshots, you'll only be able to invite public accounts that follow you to co-author a tweet. These users will need to accept your invitation. And when published, Twitter will share the tweet with followers of both accounts. Both of your avatars will be displayed at the top of the post. As The Verge pointed out, there are hopefully safeguards to prevent being hit by requests to co-author spam tweets.