Three AI Agents, One Spec

There’s been a steady undercurrent of people switching tools lately. Copilot to Claude. Claude to something else. Codex quietly entering more workflows. A lot of confidence in different directions, often delivered with certainty. I had just signed up for Claude to evaluate whether it could realistically replace ChatGPT in my workflow. Copilot already lives inside my IDE and has been solid for a while. ChatGPT fills the thinking space outside it. Codex was new to me, and I hadn’t pushed it beyond small experiments. Rather than rely on opinions, I wanted to see how they behaved when given the same real problem. I took a feature from a production side project and gave the exact same specification to all three. No prompt tuning between runs. No follow-up corrections. Just the same instructions, copied and pasted. The project itself isn’t the focus, but for context it’s a 3D print cost calculator that’s been live for some time. The feature came directly from user feedback: support multiple