This new tool adds a button to the top right corner of threads. If you click it, you'll be notified when additional tweets are added to the thread. Because you do not need to "heart" or comment in a thread to receive updates, this could add a bit of anonymity. There is no indication yet if Twitter wants to deploy the change platform-wide, though.
Earlier this week, the company released its experimental beta testing app, Twttr, which will let new adopters test new Twitter features. First, it's giving threads a chat-like look with color coding and indentation. At the beginning of the month, it retains its unwanted replies en masse (this was also discovered by Wong). In February, we learned the company is testing a way to preview user profiles without leaving your timeline. It's also testing on "original tweeter" label, which will show a thread, and it's a chronological timeline button on Android. Finally, at SXSW, Twitter makes a new camera for the app, which makes it easier to share photos and videos.
The "subscribe to conversation" button is clearly part of a larger trend. Twitter's quick confirmation is in line with what Sara Haider, director of product management, said earlier this year ̵
Twitter more conversational 🛠💬 https://t.co/jB4PWv3A04
– Twitter Comms ( @TwitterComms) March 15, 2019