Put it to work.

You've got the picture now: what Codex is, how to set it loose safely, the jobs it does well, and how to keep people in the loop. The last step is the one that actually changes anything, because reading about an agent teaches you nothing until you've watched one work on your own code. This week, you trial it. Here's the calm way to start.

Pick a few well-scoped jobs to trial

Don't reach for a sprawling rewrite to prove the point. Pick a handful of small, bounded jobs with clear done criteria, the kind from lesson three: a checkable result, low blast radius, and no production secrets in sight. Good first candidates for almost any codebase:

• Add test coverage to a module that's light on it.
• A tidy refactor with the suite as your safety net: rename, extract, split a fat file.
• A small bug with clear reproduction steps, so it can write the failing test and fix it.
• Glue code between two services, or a bit of boilerplate that follows an existing pattern.
• A small internal tool or one-off script that saves the team a recurring chore.

Write your shortlist down before you start, and make sure your repo is ready: a project instructions file with how to build, test and lint, and branch protection with a green CI as the backstop. A few real tasks beats a vague intention to "try the agent" every time.

Run the loop: scope, run, review, merge

For each job, the rhythm is the same, and it's quick:

• Scope. Write a tight brief: one clear goal, a definition of done, and the boundaries. If you can't scope it cleanly, break it down first or keep it for yourself.
• Run. Hand it to the agent and let it work in the sandbox or your checkout. Run a couple in parallel if they're independent.
• Review. Read the diff like any contributor's. Is the approach sound? Anything off? Green tests are a start, not a sign-off. This is where your judgement goes in.
• Merge. If it's good, merge it through your normal protected flow. If it came back off, tighten the brief or improve the context and run it again. That feedback is how both of you get better.

That last habit is the compounding bit. Every time you sharpen the brief or add a missing note to your instructions file, the next task lands closer to right. Over a few weeks the agent quietly clears a real slice of the well-shaped work, and your people spend more of their hours on the parts that need them.

The mindset to keep

Codex is leverage on the well-defined work. It is not a replacement for your engineers and it is not a reason to skip review, and the human check is still the thing that keeps what you ship good and safe. Let it carry the bounded, checkable jobs. Keep your hands on design, on the risky paths, and on the decision about what's worth building and what's worth shipping. That balance is where the speed is real and the risk stays low.

Keep the summary handy

To make this stick, grab the free one-page summary: what Codex is, the scoping rules, the sandbox and permissions, the secrets line, the review and CI guardrails, and a space for your first tasks. Print it, stick it by the desk, and you've got the whole course in arm's reach.