Which AI Coder is Best for RealTest? (Codex vs Gemini vs Claude Compared)

Hey Trader! If you have tried using AI for trading research, you know the trap. The first AI answer can look amazing. Then you spend the next hour:

• fixing syntax
• waiting the AI reponse
• checking the rule logic
• struggling with AI hallucination
• pointing the agent back to the right data
• rerunning the backtest
• etc. So I gave Codex, Gemini, and Claude Code the same job: Create the strategy, run the base backtest, optimize the moving-average settings, run a walk-forward test, and produce charts I could review. Which one wins? Let’s find out. Same task, same data, same budget I used the normal $20 plan for each tool. Agents were:
• OpenAI Codex, using GPT-5.5
• Gemini 3.1 Pro
• Claude Code, using Opus 4.7 Each agent worked in the same local RealTest environment and received the same trading idea. The strategy was a very simple:
• Trade SPY only.
• Buy when the 20-day moving average crosses above the 50-day moving average.
• Only buy when SPY is above the 200-day moving average.
• Exit when the 50-day moving average crosses back above the 20-day moving average. I did not choose this because it is a special edge. I chose it because a simple strategy makes the comparison cleaner.