Selected iOS users can now upvote or downvote replies that they see as part of a new feature that Twitter is testing. If you upvote a tweet, it will be shown as a like whereas if you downvote a tweet, it will not be publicly visible.
However, Twitter insists that the downvote feature is not quite like a “dislike” button as they are testing the feature to learn more on the types of replies that users find relevant so they may work on ways to highlight more of them.
The number of downvotes are not public and are supposedly only visible to the person behind the particular reply. However, the author of the original tweet will not be able to see or receive notifications on the downvotes.
This isn't quite a dislike button. In this research experiment, the thumbs down icon is a down vote that lets us know that you think the reply isn’t relevant to the conversation. We want to better understand the types of replies you do and don't find relevant in a convo.
— Support (@Support) July 21, 2021
Below the replies of a tweet, users might see an upward and downward pointing arrow, while some accounts might see a thumbs up icon replacing the “Like” button with an additional thumbs down icon next to it. Users may also see the classic heart icon, with an adjacent downward arrow.
Even though Twitter Support says that its downvote experiment is not a dislike button, accounts with the “thumbs-down” in their app feature a pop-up that explicitly states that Twitter is testing dislikes on replies. This may sound contradictory, but then again Twitter is testing this feature on its replies and not the original tweets.
I just got it too, does this mean that no one can see the numbers? pic.twitter.com/9z3cr7bbzH
— iya (@knpgitu) July 21, 2021

In the past, Twitter’s product lead has said that the social media platform was looking into adding a dislike button, so this trial could be a precursor to that. Twitter also adds that the number of downvotes will not affect the order of replies.
Downvotes aren’t public –– you won’t be notified that someone has downvoted your reply. Upvoting a reply as part of this test will be treated as a like –– you’ll be notified and the reply will show up in their Likes tab.
— Support (@Support) July 21, 2021
This feature has also drawn comparisons to Reddit, as its posts also come with an option to upvote or downvote to highlight a subreddit’s favourite posts, responses or replies. As the reason for this feature is research-based, it is unclear if Twitter will add this feature permanently in the near future.
This feature is only being tested on iOS platforms for the time being.