The Collab feature is a service that will allow two accounts to co-author the same tweet. If you use Collab on Instagram, you will know how Collab works, the option is not yet publicly available to Twitter users and this feature works only after one user accepts a collaboration request from another.
According to the screenshot shared by Paluzzi, the Twitter team wants the new feature to be such that it gives an opportunity to the creators to interact with the company, App researcher Alessandro Paluzzi has been posting evidence of the feature’s development since at least December, but recently revealed what appears to be an official dialog box from Twitter about how these tweet collaborations might work.
No word on whether Twitter will also offer collaborative tweets. But it seems likely that they will, given the similar capability of some competitors. Maybe Twitter is offering a co-authoring feature because Instagram has something similar from 2021.