Most "Codex vs Claude Code" posts are benchmarks: same prompt, two tools, a winner. We don't run them that way. We run both, every day, across four products and a set of client platforms, and each one has a job. Claude Code builds. Codex reviews. The money paths get a second, adversarial review on a stronger Claude model. This post is how that split came about and what it costs.
If you want a benchmark, there are plenty. If you want to know how a small studio actually divides the work between the two, read on.
The short version
| Job | Tool | Why |
|---|---|---|
| Orchestrating the day's work | Claude Code | It's where the tickets, the agent definitions and the standing rules live |
| Checking a ticket is true before building | Claude Code (a read-only scout) | Needs to trace callers across a codebase it already knows |
| Building a well-specified change | Claude Code (builder agents) | Fast, follows a spec, stops when told |
| Default review on feature, UI and refactor branches | Codex | A second model, with no memory of writing the code, reading it cold |
| Review on anything touching money, logins or customer data | Claude Code (adversarial reviewer) | The strongest model we have, told to find what's wrong |
| Second opinion when Claude is stuck | Codex | Different model, different blind spots |
The pattern is simple: the model that wrote the code is never the only model that checks it.
How Claude Code fits
Claude Code is the main session. It reads the ticket, decides whether a scout needs to check the premise, hands the build to a builder agent, waits for CI, and sends the branch for review. The rules it works to are written down once per codebase and loaded every time: how the product is structured, what never changes, where the tests are.
The agents under it are defined as named roles, each with a limit. A scout can read but not write. A builder stops at "pushed". A lighter builder takes small, bounded jobs so we're not spending the bigger model on an icon swap. We covered the process side in spec-driven development with AI agents.
One thing that changed in October: our builders moved to Claude's mid-tier model. We'd been running the top model for everything and the mid-tier turned out to be cheaper, faster and, on well-specified work, no worse. The top model now does the two jobs that need judgement: scouting and adversarial review.
How Codex fits
Codex is OpenAI's coding agent. We run it from the command line, non-interactively, as the default reviewer on feature, UI and refactor branches.
The mechanics: when a branch is ready, Claude Code spins up a clean copy of it, writes the review brief into the file Codex reads as standing instructions, and runs a diff-aware review against main in the background. A review takes ten to twenty-five minutes. The findings come back verbatim, ranked blocker, high, medium, low, with a file and line for each and a concrete failure case. A person reads them and decides.
The brief Codex gets is blunt: find what's wrong, don't summarise, verify every finding by reading the surrounding code, say explicitly if nothing's blocking. No praise, no restating the diff.
Two reasons it's Codex and not another Claude session:
Independent eyes. A model reviewing code it just wrote tends to agree with itself. A different model, with no context of how the code came to be, reads it the way a new team member would. It catches different things.
Load. Our Claude plan is the bottleneck. Moving the default review to a separate subscription took a large, steady chunk of work off it and gave us headroom for the builds.
Codex is also where we go for a second diagnosis when Claude is going in circles on a problem. Different model, different blind spots. That's worth more than it sounds.
What Codex doesn't get
Anything touching money, logins, document signing, uploads or keeping one customer's data away from another's goes to our adversarial reviewer: Claude's strongest model, with a brief to construct a concrete failure scenario for every finding and discard anything it can't make concrete. It checks currency handling, double counting, idempotency, tenant scoping, race conditions and silent failures, in that order.
That's not a comment on Codex. It's that for those paths we want the heaviest review we have, and we've tuned that brief over months against our own products. How the tiers work is in reviewing AI-written code that handles money.
What it costs, honestly
The tools are the cheap part. The expensive part is how you use them.
In September we ran six builders in parallel over a weekend and burned through roughly eight million tokens, most of it on conflicts between branches that touched the same files and the re-testing that followed. That weekend is why we now run at most three builders at a time, merge in a fixed order, run only the tests that cover what changed while building, and let CI run the full suite.
Splitting review across two subscriptions is part of the same discipline. One plan carrying builds and reviews hit limits. Two plans, each doing what it's good at, don't.
Rough edges
A few things we've hit, so you don't have to:
- Codex's command-line tool changed its flags. Newer versions won't take a custom prompt together with a base branch for a diff review. We write the brief into its instructions file instead and run the review with no prompt argument. If that ever fails, we fall back to feeding it the raw diff.
- Background reviews need babysitting. A twenty-minute review has to run in the background, which means something has to poll for the result and clean up afterwards. We use a very small, cheap agent for that so the expensive models aren't sitting idle waiting.
- Findings need a person. Both tools produce confident findings. Some are wrong. The review step ends with someone reading them, not with the agent applying them.
What we'd tell you
Don't pick one. Pick a job for each.
If you're a small team with one subscription, start with one tool for building and get the specs right. When review becomes the bottleneck, add a second model to review cold. And whatever you use, put the strongest review you have on the code that moves money.
FAQ
Is Codex better than Claude Code?
For us they do different jobs, so the question doesn't come up. Claude Code builds and orchestrates; Codex reviews feature branches cold and gives a second opinion. We put the strongest Claude model on anything touching money or customer data.
Why use two AI coding tools instead of one?
Independent review and load. A different model reading the code catches things the author model agrees with itself on, and splitting builds and reviews across two subscriptions stopped one plan hitting its limits.
Can Codex and Claude Code work together automatically?
Yes. In our setup Claude Code prepares the branch, writes the review brief, runs Codex in the background and relays the findings. A person makes the final call on what ships.
What does running AI coding agents cost?
The subscriptions are modest. The real cost is in how you run them: parallel builders colliding, full test suites re-run on every fix, agents left running. Limits on all three are what keep it affordable.
If you want software built this way, with a written spec, two models reviewing and a person deciding, that's what we do.
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