100 million users in a week appears, based on what I could find, to be about on par with other features Instagram has added over the years. Given that Instagram's user base has grown quite a bit since some of those other features launched, 100 million users of a new feature may actually be a poor showing, comparatively.

Indeed, Twitter is as vulnerable as Snapchat was when Stories launched, and Twitch when IGTV launched, and TikTok when Reels launched. But how vulnerable is that, really? In fact, I was just thinking about how much better Twitter's content has become lately. Perhaps Threads has served to relieve Twitter of the dregs that was bringing it down?