It can be hard to build and solve million equation models. Making them high performance, stable, and parallel? Introducing ModelingToolkit.jl! In this workshop we will showcase ModelingToolkit as a system for building large differential equation models in a hierarchical component-wise way. This acausal modeling system is reminiscent of widely used tools like Simulink and Modelica, but we will showcase how ModelingToolkit's deep integration with interactive symbolic programming leads to a more intuitive pure Julia modeling system. The audience will be walked through a live demonstration of using ModelingToolkit to compose models and add transformations, like index reduction of differential-algebraic equations (DAEs) and tearing of nonlinear systems, to improve stability and performance of the generated code. We will demonstrate how to use the automated parallelism easily solve millions of equations in the most performant way. We will show how ModelingToolkit extends far beyond differential equations, featuring how it can be used for similarly generating high performance code for nonlinear optimization, solving nonlinear equations, doing nonlinear optimal control, generating models from chemical reaction descriptions, and more. The user will leave with a better understanding of the growing symbolic-numeric modeling ecosystem and the future of large-scale accurate and high-performance SciML modeling.