The social media company made the announcement on its own platform with a tweet. As part of the announcement, Twitter says this is a limited experiment on iOS. So you’ll likely won’t see the prompt at all until a wider rollout, if it happens.

— Twitter Support (@TwitterSupport) May 5, 2020 For now, the criteria for “harmful” replies is murky at best. There’s no indication as to what constitutes as harmful. But from the language used in the tweet, it sounds like these “harmful” replies will ultimately still be allowed on the platform. Then there’s the question of if the prompt will only show up for replies, or original tweets themselves. At any rate, if you’re using Twitter on iOS and you see this prompt when replying, this is the reason behind it. As mentioned earlier, this is part of a limited experiment. For now, there’s no word on what’s the experiment period, or if the test will be rolled out to more users, and on other platforms. (Source: Twitter)