On October 31, Ryan Madden — an independent tester who keeps putting language models through Factorio — posted a new result: OpenAI's GPT-5.6 Sol, running inside Codex at a low thinking level, completed a peaceful run (no biters) of the game in 13.5 hours of game time, ending with a rocket launch. The headline is not the finish, though; it is how the second half was won: not by planning, but by brute-force hauling.

It does not watch the game; it writes code against it

Madden's harness pairs a game manager with a small library — Python this time, where the earlier Claude Code attempt had used Bash. The model plays programmatically, but the library enforces the exact restrictions a human GUI player faces: player reach and fog of war. No x-ray vision, no remote building. Sol had to decide inside the same information and action constraints as a person, on a low thinking-level budget. Madden has been polishing this pipeline for a while — he previously built Faketorio, a dedicated agent testbed for the game.

From "cannot use belts" to reaching the late game

The baseline is the previous generation: GPT-5.5's attempts collapsed because it failed to use transport belts at all — and belts are the foundation of Factorio logistics. GPT-5.6 Sol not only used them; through the blue science stage it ran efficiently enough to surprise Madden, who had planned to terminate the run there and instead let it continue. The run manager recorded production statistics throughout, leaving a full curve of output against research milestones.

But the rocket was hauled into orbit

The late-game weakness arrived on schedule: as the factory scaled, production systems failed to connect, and relative progress slowed sharply. The final rocket launch was achieved through significant "manual" effort by Sol — repeatedly ferrying supplies between areas of the factory to paper over the disconnected systems. That is the most interesting detail of the whole run: the model would rather haul forever than step back and restructure. On cost, Madden told RuntimeWire in an email: about 250 million input tokens (95% cached) and 1.5 million output — roughly $52 at API pricing.

So what

Madden's own framing is worth quoting: in many ways Factorio is analogous to programming, but far more legible to casual observers, which makes it a convenient medium for grounding discussion of model behavior. This run shows the current shape of agents — locally smart, globally makeshift: able to patch, not yet able to architect. The day a model chooses to rebuild the factory instead of hauling forever is the day it has actually learned long-horizon tasks. Madden says he will next test other models, higher thinking levels, and non-peaceful runs — a series worth following.

Source: https://ryanmadden.net/gpt-56-beats-factorio/
Coverage and cost figures: https://runtimewire.com/article/gpt-5-6-sol-s-factorio-rocket-run-used-250-million-tokens-about-52-at-api-prices