Dynamiqs is a high-performance Python library for simulating quantum systems, built on JAX for GPU acceleration and automatic differentiation. It provides solvers for the Schrödinger equation, Lindblad master equation, stochastic master equations (diffusive and jump), and Floquet integration, with support for time-dependent Hamiltonians, batching over parameters, and gradient computation (including Hessians). The architecture is modular: an abstract integrator hierarchy (with concrete solvers using Diffrax, matrix-exponential, low-rank, Rouchon, and Monte Carlo methods), custom quantum array types (dense and sparse diagonal DIA layout), a clean `TimeQArray` abstraction for time-dependent operators, and utilities for state/operator construction, plotting, and quantum information metrics. The library is designed for quantum optimal control and parameter estimation, and is used in production at Alice & Bob. It features extensive automated tests (including numerical gradient/Hessian validation) and is actively maintained with a growing community.