We are running 21 million cells, and our machine is using ~18-21 GB of memory. For 40 time steps, it takes about 24-27 hours. Several of those hours are spent initlializing, so I’m not surprised about it taking a while to initialize on your machine. We are using spatial multipliers for many transitions, as well as transition targets, so that may affect run times and/or memory some too. I’d be happy to talk with you more about our experience and/or try to run your model with your inputs on my machine to test memory usage if that would help. My machine has 24 GB memory.