One-prompt galaxy collision benchmark: Opus 5 beats Fable 5.1, GPT-6 Astra finishes last
Fleischkluetensuppe · reddit · 2026-09-12
A Reddit user ran the same concise prompt ("Create a simulation of the milkyway andromeda collision") through three models, spending roughly $5 in tokens each, and open-sourced the results as the milkyway-andromeda-merger-bench on GitHub.
- Opus 5 and Fable 5.1 both produced single-file JavaScript particle simulations with dynamic, physically plausible galaxy motion; the author found Opus 5 the best-looking, edging out Fable 5.1.
- GPT-6 Astra went for a full React project with boilerplate, and its physics simulation was very static — clearly the weakest of the three.
The takeaway: on one-shot complex simulations, models that focus on a single self-contained file beat those that over-engineer with scaffolding.
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