Install

openPASO is not useful on its own

openPASO is the part that drives the solvers. The thinking is done by an AI model, which you bring. Before you install, know which of the two ways below you will use. The install itself is the same either way.

	Option A: an AI app	Option B: your own API key
You need	Claude Code, Claude Desktop or Cursor	an account at openrouter.ai
Extra cost	none beyond your subscription	you pay for what you use
Choice of model	whatever the app offers	any model on OpenRouter
Good for	trying it out, everyday work	scripting, experiments, cheap models

Not sure whether your app works? If you have Claude Code, type claude mcp list in a terminal. If the command exists, use Option A.

What you need

• Python 3.10 to 3.13
• at least one solver. You do not need all nine; openPASO tells you what is missing and how to get it.

Check your Python:

python3 --version    # 3.10, 3.11 or 3.12: go straight on. 3.13: read the box below.

On Python 3.13 you need a C compiler

The install takes about two minutes longer. openPASO keeps numpy below version 2, because the preCICE coupling library requires that, and for Python 3.13 no ready-made numpy below version 2 exists, so pip has to compile it.

• Debian or Ubuntu: sudo apt install build-essential
• macOS: xcode-select --install
• Fedora or RHEL: sudo dnf install gcc gcc-c++ make
• Windows: install Build Tools for Visual Studio with "Desktop development with C++", or, much simpler, install Python 3.12 from https://www.python.org/downloads/.

Without a compiler the install stops on numpy with Unknown compiler(s) and metadata-generation-failed. Python 3.14 and newer are untested.

If your Python is older than 3.10 or newer than 3.13, install a supported one beside it. They live side by side without conflict. With conda: conda create -n paso python=3.12 && conda activate paso.

Install openPASO

git clone https://github.com/Hereon-InstituteMS/openPASO.git
cd openPASO
python3 -m venv .venv && source .venv/bin/activate
pip install -e .
pip install scikit-fem            # the easiest solver to start with

Then install the agent packages. Only Option B uses them, but installing them now costs nothing:

pip install -r langgraph_eval/requirements-langgraph.txt

Windows

Use python -m venv .venv and then .venv\Scripts\activate. A few other commands differ: copy instead of cp, dir instead of ls, set instead of export. openPASO is developed and tested on Linux. It should work on Windows, but we do not measure that, and the solvers that build from source (4C, SPARTA, deal.II) are the least likely to.

More solvers

Each solver has its own page with the exact install command and what openPASO knows about it: see Solvers. In short:

pip install ngsolve scikit-fem meshio      # into the same .venv
pip install KratosMultiphysics-all         # Kratos: use the -all package
pip install dune-fem mpi4py                # DUNE-fem: mpi4py is a hidden requirement
conda create -n fenics -c conda-forge fenics-dolfinx   # FEniCSx: its own conda environment

Any export NAME=value line only lasts until you close the terminal. To keep it, add the same line to the end of ~/.bashrc (or ~/.zshrc).

If a solver will not install, ask openPASO once it is connected:

How do I install 4C on Ubuntu? Use the knowledge tool.

Next: check that it works.