Its growth has been pretty amazing in the last year. I mean, it's been so fast that no one even knows how to plan for it anymore. We setup a meetup in Denmark expecting 20 people to show up and then had to change reservations because 70 people showed up, then ran some extra workshops, then setup
http://www2.compute.dtu.dk/~apek/SCIML2022/ for a 30 people week long course, and then had to petition to remove the cap and change rooms to accommodate the 120 sign ups! And that's all just one piece of just this summer: I haven't had a home since August because there are so many massive Julia events overshooting their enrollments that I've just been hopping UK, France, Germany, Norway, Sweden, Denmark, Dallas, Colorado, Maryland, Florida, California, Greece, Italy, ... with each thing having more interest than organizers could accommodate. This year has been absolutely insane and the number of people in the post-covid world is so drastically different that no one really knows how to put on events of this size. It's been an absolutely amazing though rather hectic thing to experience. I don't know if you could call it fastest growing, but it's at least been exponential and faster than most people can realize until you show up somewhere since every case has blown expectations by a few times.