Twitter is testing a new feature that allows twitter users to view analytics directly from the tweet. Users will see a “View analytics details” below tweets.
It is possible that this feature is only showing up for verified users, as the screenshot that the verge have shows it being on a verified users Twitter account.
The Verge was the first to report the feature and included this screenshot.
The data comes from Twitters Analytics, which is free to all users at analytics.twitter.com. Details include specific analytic data on each individual tweet, including impressions, engagement and engagement rates. It also includes information about two viewed a photo that was treated as well as showing how many Twitter users expanded the tweet
The feature appears to only be available for mobile users at this time, likely because there is no current integration between twitter analytics and the mobile app at this time.