Have you used almost any ODE solver? Almost every single one uses embedded methods to adapt time steps. ode23, ode45, ode23t, ode23tb, ode15s, LSODE, LSODA, radau, rodas, VODE, CVODE, ... even for DAEs you have DASSL, IDA, ... I can keep going but it's just listing every ODE solver code out there. Once you do that then the computation is dependent on values and thus the full compute is not determined by the input sizes, which is something known to be blocking the full usage in Jax because of XLA limitations (for example the implementation of dense output).