The number of active Mastodon users — those who've logged in in the last 30 days — has fallen to 1.8 million from a high of 2.6 million. This reflects the fact that while there's a wave of new users after each Musk tantrum, the majority aren't sticking around. Even the 1.8M figure is inflated by new accounts, so I expect a further drop.
Still, the number of active users is over 4 times what it used to be before the Twitter takeover.
Source: https://api.joinmastodon.org/statistics (and Wayback machine).
@randomwalker If "active users" are determined by them recently posting, then it's not a great metric. Twitter measures by how often a user connects while logged in, and on Mastodon there's no way to aggregate that data.
Most social networks have more lurkers than active posters, so I would at least double that number and assume that people are sticking around without contributing much.
Maybe an admin of a larger instance could provide better stats on that based on the behavior of their users.
@Alex Activity is not based on posting, but based on being logged in. Logged-in status is not publicly visible, of course, but my understanding is that it is reported in aggregate by Mastodon servers.