How to use Claude to rewrite a space simulation in Rust
The author reports a Rust/Bevy sandbox running into the thousands of simulation agents. A 100,000-agent target remained unachieved, and the sandbox had no game objective.
news.ycombinator.com
Prompt to try
Editorial adaptation, not the source author’s exact prompt. Replace bracketed inputs and review tool permissions first.
Help rewrite [Elixir/Phoenix simulation] in Rust to address [observed platform issue]. Keep the simulation core synchronous and IO-free, embed it in [Bevy client], and evaluate [agent counts]. Clearly distinguish achieved scale from future targets.
Reach people exploring AI agents
See placements →What happened
The author reports a Rust/Bevy sandbox running into the thousands of simulation agents. A 100,000-agent target remained unachieved, and the sandbox had no game objective.
Reported by kalcode on Hacker NewsHow the agent did it
- Built an initial Elixir and Phoenix space-economy prototype with Claude.
- Asked Claude to rewrite the engine in Rust after Windows scheduler issues.
- Embedded the pure simulation core directly in a Bevy client.
Where a person stepped in
The author selected the rewrite and tried higher simulation counts; the post does not describe formal code review.
A person approved each step before the agent continued.
A developer paired with Claude to build a space-economy simulation they had wanted to explore. The sandbox contains autonomous ships whose planners choose activities such as trading, taking delivery contracts, refueling, retrofitting and docking for crew rest. Markets respond to supply, while factions, migration and abandoned stations add other changing conditions.
The project started as an Elixir and Phoenix prototype. When the BEAM scheduler struggled on Windows gaming PCs, the developer asked Claude to rewrite the engine in Rust. The resulting simulation core is described as pure, synchronous and free of input/output, with its own hecs entity-component system. A Bevy client embeds the core directly as a library, sharing one world between simulation and rendering.
The author reported roughly 485 simulation agents and said they had pushed the count into the thousands with acceptable operation. Reaching 100,000 remained a struggle and a target rather than an achieved result. The project was a sandbox without an objective, and the author was not actively pursuing a shippable game. Who it's for: developers exploring simulation architecture and agent-assisted rewrites of experimental game systems.
Prompt
Suggested prompt (written by Agents In Use, not the author's)
Source: Hacker News · kalcode
Frequently asked questions
Why was the engine rewritten in Rust?
The author says the Elixir/Phoenix prototype’s BEAM scheduler struggled on Windows gaming PCs, so they asked Claude to rewrite the engine.
Was the simulation a finished game?
No. The author calls it a sandbox without an objective and says they are not actively pushing it toward a shippable game.
More details
Remaining steps
- Pushed the simulation agent count into the thousands.
About this account
Claude supported paired development and rewrote the engine in Rust at the developer’s request.
Platform: Hacker News. Attribution: https://news.ycombinator.com/item?id=48996187. Prompt: Suggested (written by Agents In Use, not the author's). Sourced by the Agents In Use pipeline.
Credit: kalcode on Hacker News
Source published 21 Jul 2026
Source checked 14 Oct 2026
Tools and topics
Claude · Elixir · Phoenix · Rust · hecs · Bevy
Rust · Bevy · Simulation
Editorial completeness: 100/100. Measures documented fields, not agent performance or verified outcomes.