Less active than Mastodon, I'd assume more active than Nostr.
But the interesting thing for me isn't activity — it's the people on there.
Of the cohort who had >100k followers on Twitter, I think more of them post regularly on Bluesky than post on Mastodon. Bluesky definitely has a more cohesive feel, especially because there's currently just one instance & mod team.
I'm a donating supporter of the Mathstodon.xyz instance, but (sadly?) most of "math Twitter", at least the education-focused university faculty, ended up on BlueSky. I think there's a strong appeal for "a straight forward Twitter clone without Musk" for a lot of people.
Mastodon, and the Fediverse in general, make user interaction decisions on purpose to limit many of the issues common to social media. Think about: mob culture, addiction, and the like.
I wonder if BlueSky intends to follow on those. For example, hiding user actions counts (repeats, favourites, etc...) until the user acts on one.
Things like these may be strange for those accustumed to Twitter, but personally, is what makes me stick with smaller instances on the Fediverse.
My bet is regardless of any initial good intentions, since BlueSky is a company, market pressures will inevitably force them into dark patterns like we see on every other commercial social network (going back to the early days of the companies, Facebook, Twitter, and even Google looked really good early on until all were corrupted by profit motive). My belief is that the profit motive is necessarily at odds with free communication.
To me, the ActivityPub network (Mastodon and friends) is relatively unique in the social media space in having no direct commercial pressures (the protocol is developed by W3C) and therefore being inoculated against the causes for these dark patterns.
I don't know about nostr, but I find it is a lot less active than Mastodon. In general the tech accounts I am interested in have moved to Mastodon rather than bluesky. I imagine this would depend on whose activity you are interested in, and where they have chosen to migrate to
Bluesky is much smaller than Mastodon, but how active it feels will depend on who you're following. It also has an Algorithm (TM); I never really missed this when I went from Twitter to Mastodon as I mostly used the linear timeline anyway, but I gather that some people find that Mastodon feels empty/inactive without one.
They’re all just arbitrary ghettos that aren’t dissimilar to each other. None of them matter in terms of influence but are like nice Reddit boards for certain interests.
But the interesting thing for me isn't activity — it's the people on there.
Of the cohort who had >100k followers on Twitter, I think more of them post regularly on Bluesky than post on Mastodon. Bluesky definitely has a more cohesive feel, especially because there's currently just one instance & mod team.