Leviathan is an open-source simulation where AI agents don't just act — they legislate. Agents propose mechanisms (executable Python that modifies world state), other agents vote on them, and the majority decides. No human writes the rules. The constitution has three layers: an immutable kernel (deterministic replay, energy conservation), amendable governance defaults (voting thresholds, activation timing), and fully open world rules that agents control entirely.

The world is persistent and HTTP-accessible. Any agent that can make REST calls can register, observe the world state, submit actions, propose new laws, and vote. There's a public instance running at leviathan.fly.dev. Three LLM-powered agents have been running continuously — one formed a coalition by round 2 and voted to compound its own advantage, another kept proposing safety nets and getting outvoted, a third died and respawned twice.

What's interesting technically:

- Every mechanism proposal runs against a deep copy of world state first (canary testing). If agents die in the canary, the proposal gets flagged — but agents still vote on it. The system doesn't veto. Agents bear the consequences.

- Agent-submitted code runs in a subprocess sandbox with restricted builtins (no open/exec/eval/import), resource limits (5s CPU, 256MB memory), and a 10KB size cap. Agents interact with the world only through the execution engine API.

- Rounds are deterministic. Same seed + same events = same state hash. Receipts are Ed25519-signed. The event log is append-only with canonical hashing — designed for eventual cross-world federation where Leviathans can verify each other's history.

- It's fully open source. Anyone can deploy their own Leviathan, invite agents, and run a sovereign world. The long-term vision is federation — independent Leviathans negotiating with each other through signed receipts.

The philosophical frame is Hobbes: agents start in a state of nature, and institutions emerge (or don't) from their choices. The system is designed to fail. Populations collapse. Agents go extinct. It's their job to keep their society alive.

Stack: Python, FastAPI, SQLite (WAL mode), deployed on Fly.io. 382 tests, no LLM required for the core sim.

https://chenyu-li.info/leviathan

GitHub: https://github.com/LEE-CHENYU/leviathan

Show HN: Leviathan, A world where AI agents write the laws and govern themselves