Vibe Check: Codex—OpenAI’s New Coding Agent
🎧 🖥 Bonus: A special episode of AI& I ___with OpenAI product team member_Alexander Embiricos is now live. Watch on X or YouTube , or listen on Spotify or Apple Podcasts.
Last night I shipped a new feature for Cora , Every’s AI-enabled email assistant. Cora is not a vibe-coded product: Its codebase is a 5,500-plus commit cathedral of Rails craftsmanship mostly from Kieran Klaassen , Cora’s general manager, our resident DHH. Needless to say, exactly zero previous commits are mine.
Undaunted (or somewhat daunted, but holding my shit together), I pressed “merge” on a pull request for a little quality-of-life UI update, and what had previously been just a twinkle in my eye appeared on production in less than an hour. How?
I used Codex—OpenAI’s new coding agent, launching publicly as a research preview today. Like Devin , Codex is designed as a software engineer that can build features and fix bugs autonomously. OpenAI has tried to incorporate the taste of a senior software engineer into how Codex writes code: It’s familiar with how large codebases work, and writes clean code and commit messages. It’s designed for you to run many sessions in parallel, so you can manage a team of agents without touching a single line of code.
In OpenAI’s storied tradition, Codex is confusingly named. The company has previously used the same name for both a model and a command-line tool. (Here’s an o3 summary of the full history of OpenAI’s use of this name.) It’s a little rough around the edges and balkanized into a product separate from ChatGPT (more on this later). Even so, it’s useful.
We’ve been testing it for the last few days at Every. What follows is our day-zero vibe check. I invited Kieran to help me write this review because Codex, unlike many other AI coding agents, is clearly built for senior engineers like himself, and I think his perspective is important.
I also had a chance to speak to the member of the OpenAI team responsible for Codex, Alexander Embiricos. You can check out our full conversation here:
Let's go through what it is, how it works, what to use it for, and what it means. But first: the Reach Test.
The Reach Test: Do we use it every day?
The best leading indicator for long-term usefulness of an AI product is what I’m calling the Reach Test: Do I find myself automatically turning to this tool to do certain tasks? Or do I just leave it on the shelf and forget it’s there?
Here are the results of our Reach Test on Codex:
- Kieran (agent-pilled tech lead archetype): Yes, he’s thinking about how to use it all day and night.
- Dan (technical tinkerer CEO, weekend vibe coder archetype): No, but because I’m normally coding on net new ideas rather than existing products.
Overall: It’s a tool you’ll reach for if you’re a tech lead adding features or fixing bugs on an existing codebase. If you’re trying to vibe code a new one-person billion-dollar SaaS company , look elsewhere.
A Codex tour
Codex presents you with a simple text box that asks you to describe the programming task you want it to perform, followed by two buttons: “Ask” and “Code”: