Twitter is testing a new system where some iOS users may see different configurations of upvote and downvote, or like and dislike buttons on replies to a tweet, rather than just the traditional like button.
According to Twitter, this test helps them understand the types of replies that are relevant in a conversation, and show them more. Twitter says that upvote actions will count as likes on your profile, while downvote actions will not be made public.
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The company also said that the experiment is just for research at the moment, and does not count as a dislike button because it won’t actually change the order of tweets.