The big change is finally here. Twitter usernames will no longer count towards the 140 characters limit. With this new update, all users will get 140 characters, entirely, for their tweet replies.
Users can now reply to tweets and tag as many usernames as wanted. These usernames will not add up to the 140 characters limit on the tweets.
While this is works for reply tweets, it is important to note that this will not be the case for tweets that are public (non-reply tweets).
Twitter has enabled this feature to all the users and is currently being rolled across Twitter web and mobile apps. There needs to be no update to be done at the user-end. This new feature (not really) will be available for all users without requiring an app update.
Noticeably, this feature completely strips out the usernames in your reply tweets. Instead, the people involved in the conversation will be shown just above your reply message. Like so.
This feature is supposedly aimed at improving user’s experience, by allowing more characters for their thoughts. But, I think otherwise. This might bring in a load of spam tweets from various users. There is no clear thought on how Twitter aims at tackling this. Official announcement.