SystemOneHarness
The System One harness for System One models. Run Jev and other System One models locally or directly on HarnessRouter.ai.
207 ★ on GitHub
What it is
Turn a System One decision model into an agent loop. System One Harness observes an environment, compiles its finite action space into typed questions, gates each decision by confidence, executes the chosen action, and records the complete trace.
Getting started
From the README:
git clone https://github.com/HarnessRouter/SystemOneHarness.git
cd SystemOneHarness
pip install -e .
export OPENROUTER_API_KEY=sk-or-... # or TYPESAFE_API_KEY=...Where the decision sits
SystemOneHarness calls the hosted decision API rather than running its own weights. That keeps the project small and means its behaviour moves whenever the vendor ships a new model version. It also means an API key and a network round trip sit in the path of every decision.
Models it references: Jev.
How active it is
Created 2026-09-19, last pushed 2026-09-21, 207 stars and 23 forks when we read it on 2026-11-02. Everything in this category is weeks old at most, so a stale push date means something different here than it would on a mature project. Check the repository before you depend on it.
Find out what your data actually supports
We turn your historical decisions into a frozen test set, then tell you which model, which threshold, and how much of it you can safely automate.