After some Twitter users began noticing a new icon when looking at tweet replies, Twitter’s Support account admitted that it’s testing a new idea (for Twitter): upvotes and downvotes. According to the announcement, this is being used as a way for the platform to better understand what kinds of replies they consider relevant to a conversation.
Twitter Support went on to explain that upvotes and downvotes are currently just being used “for research” and won't necessarily become a standard feature. It's also stated that downvotes will not affect the order of replies, and will not be publicly visible—though upvotes will appear as likes. Twitter Support was also insistent that downvotes are definitely not dislikes, a statement that many, many users are skeptical of.