The East Coast Rationalist Megameetup has existed in one form or another since 2014, held in New York City the weekend of Secular Solstice. It's been growing steadily since then, and last year we successfully made the transition to a conference hotel. That means the size of the meetup is no longer constrained by the format of the venue, since we can just get a bigger hotel if we know how big we need it to be. Thing is, I need to reserve a venue well in advance.

Rationalist or rationalist-adjacent events loosely in this style can be hundreds of attendees in size. (LessOnline, LessWrong Community Weekend, Manifest, Vibecamp, etc.) Every previous East Coast Rationalist Megameetup I've run has sold out, or was on track to sell out if I'd been set up to keep taking registrations. Last year there were a hundred and twenty people registered, and about half a dozen who emailed me asking if there was space for more. People wanted more space, and I just wasn't set up for it because I'd already scaled things up from last year and didn't know how far to scale things.

Hence the question: How many people should I assume will attend? This question will resolve either to the total number of registered attendees (for the peak attendance, if we wind up doing per-day tickets) if we don't sell out, or to one higher than whatever the maximum number of registrations the venue I wind up going with will support. (That is, if the venue would support 150 people, and the megameetup sells out all 150 tickets, I'll assume I should have gotten a venue that would support 151 people and resolve to 151.)