Same Model, Different Experience
Here’s an odd thing: use GPT-4 with OpenAI’s Codex CLI and you get decent results. Use GPT-4 with Anthropic’s Claude Code and you get better results. You’d expect a model plus its own vendor’s agent to be the best combo — but it actually underperforms paired with a competitor’s agent.
The common assumption is that Claude Code just has a better prompt. Prompts matter, but they’re not the deciding factor. Claude Code’s source reveals something more fundamental: it’s not a prompt wrapper. It’s a full agent runtime. This framework understands the model’s capability boundaries, tool execution risks, context compression strategies, and intent flow. The model is the brain, and Claude Code is the body. The analogy is rough, but it captures the core relationship.