Rails Agent Benchmark: Claude Opus 5 Most Accurate, GPT-5.6 Luna Best Value
sergeykarayev · x · 2026-08-14
The Evil Martians team released a benchmark report for Rails coding agents. They selected 8 frontier models and tested them on 21 atomic tasks (covering bug fixes, security findings, and feature requests).
Key Findings:
- Most Accurate: Anthropic's Claude Opus 5 leads by a hair, solving 92% of runs (58 out of 63).
- Cheapest & Fastest: OpenAI's GPT-5.6 Luna stands out, costing only $0.91 combined for all 63 runs, with a median run time of 3.3 minutes.
- Best Overall: GPT-5.6 Sol strikes the best balance between accuracy (84%), cost ($0.52/run), and speed (5 mins/run).
The report notes that price no longer strictly predicts score; Luna costs 1/132th of Opus but the accuracy gap isn't massive. Furthermore, a model's familiarity with specific framework APIs is a critical determinant of its performance.
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