I think it's a combination of things. There are real users who have migrated to Lemmy because of reddit's horrible treatment of its users and there are also bots being created but that's normal on the internet.

@DerWilliWonka @1337tux yeah, I'm guessing a lot, I didn't save the post, but I saw earlier this week some instances that were spun up brand new and in less than an hour had >5,000 users.

One of many reasons to recommend against allowing open sign-up on your instance. A lot htat have been around for longer, like lemmy.ca, require you to request an account, and answer some questions (like why do you want your accoutn on this particularl instance) and a real person clicks the check-mark button.

Some new users will be annoyed by such, but the truth is if they are annoyed by that, they probably aren't going to be good fedizens open to following good netiquette anyway.

I asked the same question. The answer is that there are a bunch of instances (probably 15-20) which have thousands or tens of thousands of new accounts (<1 week old) but have barely dozens of posts. Here's a sheet made by @sunaurus showing the effect. A bunch of the explosion is in open signup (no email, no captcha, no verification) and there is zero interaction on the instance. Could we be seeing half a million lurkers on instances with <200 comments combined between them in the last couple of days? I suppose it's possible, but it seems unlikely.

Experience, mainly.

I used to run a phpbb forum, on average the bot signups outnumbered the real people 10 or 20 times. And that was with some fairly robust anti spam measures in place - something I think this platform is too new to have properly sorted out yet.

I may be wrong, I don't know how the back end here works, but any place where people can post publicly will be infested with bot signups very quickly. The only real variable is how good the anti spam measures are.