Key Takeaways
• The best first reviewer is usually the model that did not write the change.
• Keep review read-only, require file-level evidence, and let the original writer own fixes.
• Stop after two review passes. Tests, CI, and an accountable human remain the release authority.
Claude Code should review Codex when Codex wrote the change. Codex should review Claude Code when Claude wrote it. That is the practical default. The point is not to crown one permanent winner. It is to separate implementation from critique so the reviewer approaches the diff without defending its own earlier choices.
This is a workflow recommendation, not proof that two models always beat one. A second model can catch a missed edge case, but it can also repeat the same assumption or invent a false positive. The value comes from independence, constrained permissions, explicit evidence, and a stopping rule.
The product names will keep changing. Model releases, benchmark claims, and plan pricing expire too quickly to serve as durable selection rules. This guide relies on current official workflow documentation and avoids a fixed model ranking.
Editorial note: This page was updated and fact-checked on August 4, 2026 against the current official OpenAI and Anthropic documentation linked below.
Quick Answer: Pick the Reviewer by Authorship
| Situation | First reviewer | Why |
|---|---|---|
| Claude Code wrote the diff | Codex | Independent review is directly supported by Codex review tools. |
| Codex wrote the diff | Claude Code | A restricted Claude reviewer can inspect the change in a separate context. |
| Human wrote the diff | Either, then switch if needed | Choose the reviewer with the clearest repository context and domain instructions. |
| High-risk change | Both, sequentially | Use distinct scopes, then escalate disagreements to a human owner. |
| Small, low-risk change | One independent reviewer | More agent passes can cost more than the risk justifies. |
Authorship is only the default. If one tool has the repository instructions, test environment, or specialist context the other lacks, that evidence can justify a different order. Write the exception down so the workflow stays auditable.
Why Independence Matters More Than a Model Ranking
Review independence means the reviewer receives the request, diff, checks, and project rules without inheriting the writer's need to defend its own implementation.
Review is a different job from implementation. The writer tries to satisfy the request and make the checks pass. The reviewer tries to falsify that result: find an unhandled input, a contract violation, an accidental behavior change, or a test that proves less than it appears to prove.
OpenAI documents a dedicated Codex review flow that reads a selected diff and returns prioritized findings without changing the working tree. It can review changes against a base branch, uncommitted work, a commit, or a custom scope. See the official Codex code review documentation.
Anthropic documents Claude Code subagents with their own context, system prompt, tools, and permissions. Its examples include read-only exploration and code-review roles. See the official Claude Code subagent documentation. Those capabilities make a separated reviewer possible in either direction. They do not guarantee a correct verdict.
The Five Quality Gates
1. Scope Gate: Freeze the Review Target
Give the reviewer one explicit target: the current uncommitted diff, one commit, or the branch against a named base. Include the acceptance criteria and repository instructions. Do not ask for a vague review of the entire codebase unless that is truly the task.
A useful scope statement is: Review this branch against main for correctness, security, regressions, and missing tests. Do not edit files. The same discipline powers a strong AI content pipeline: each gate has a defined input, output, and failure condition.
2. Baseline Gate: Run Deterministic Checks First
Run the closest tests, type checks, lint rules, and build before paying a model to infer what the tools can prove. Record any pre-existing failure. Otherwise the reviewer may attribute old breakage to the new diff, or spend its context describing a compiler error you already had.
3. Evidence Gate: Reject Unsupported Findings
Every actionable finding should name the file and location, explain the failure mode, identify the affected input or caller, and recommend the smallest safe correction. A preference such as "I would structure this differently" is not a defect unless it violates an explicit project rule.
This is the coding equivalent of the evidence checks in AI content scoring. Severity labels are useful only when they change the decision. High means block release. Medium means fix or consciously accept. Low means optional improvement.
4. Fix Ownership Gate: Return Findings to the Writer
The reviewer should not silently repair its own findings. Send valid findings back to the original writer, because that agent holds the implementation context and can update tests with the fix. Then rerun the deterministic checks before the second review pass.
5. Stop Gate: Cap the Loop
Stop after at most two review passes when no new high-severity evidence-backed finding appears and all required checks pass. If the models disagree, capture both claims and ask the human owner to decide. Never let two agents debate until one yields.
When Claude Code Writes, Let Codex Review
Read-only review is a review pass that returns evidence-backed findings without modifying the working tree.
This direction has the most direct bridge. OpenAI maintains the Codex plugin for Claude Code. Its /codex:review command performs a normal read-only review, while /codex:adversarial-review supports a more challenging, steerable review for riskier decisions.
- Ask Claude Code to implement one scoped change and run the required checks.
- Inspect the diff and confirm there are no unrelated files or secrets.
- Run the Codex review against that diff with the acceptance criteria attached.
- Have Claude Code address only evidence-backed findings.
- Run checks again, then allow one final Codex pass if the fixes were material.
The plugin also offers an automatic review gate. Its own documentation warns that a stop hook can create long-running Claude and Codex loops and drain usage. Use that gate only with a hard pass limit and a clear failure handoff. A scheduled automation needs the same protection.
When Codex Writes, Let Claude Code Review
Fix ownership means the original writer remains responsible for applying accepted findings and rerunning the deterministic checks.
Use a dedicated Claude Code reviewer subagent or a plan-only session. Deny edit and write tools. Give it the same diff, acceptance criteria, project instructions, and baseline results. Anthropic's CLI reference documents plan permission mode and tool restrictions, while the subagent documentation shows how to define a specialist reviewer.
ROLE: Independent code reviewer. SCOPE: Current branch against main. PERMISSIONS: Read-only. CHECK: Correctness, security, regressions, missing tests. RETURN: Severity, file and line, evidence, smallest safe fix. IGNORE: Style preferences that do not violate repository rules.
Do not provide the writer's hidden chain of reasoning or ask Claude to validate Codex's confidence. Give it the artifacts that matter: request, diff, tests, logs, and explicit constraints. Independent context is the feature.
When Both Models Should Review
Two sequential reviewers can be justified for authentication, billing, permissions, destructive migrations, public API compatibility, or large dependency changes. Split their assignments so they do not simply echo each other.
| Reviewer scope | Questions to answer |
|---|---|
| Correctness reviewer | What input, branch, or state transition produces the wrong result? |
| Security reviewer | What trust boundary, permission, secret, or destructive action changed? |
| Regression reviewer | Which existing consumer or contract can the diff break? |
| Test reviewer | Which claim is untested, and what assertion would prove it? |
Run them sequentially or in separate worktrees. Never allow simultaneous writes to the same checkout. Separate worktrees make attribution and rollback clear, while a single fix owner prevents two partial solutions from colliding.
What Cross-Model Review Cannot Replace
- Tests: a plausible explanation is not executable evidence.
- Static analysis: a model should not duplicate deterministic rules.
- Repository policy: both tools must follow the same checked-in instructions.
- Human accountability: a person still owns risk acceptance and release.
- Production observation: monitoring and rollback remain necessary after merge.
If you want reusable reviewer instructions, start with a small skill rather than a giant universal prompt. The Claude Code skills guide explains how to package focused workflows. For an example of hard quality gates, see the Claude Blog delivery contract.
Final Verdict
Use the other model as the first reviewer. Claude Code reviews Codex output. Codex reviews Claude Code output. For high-risk changes, use both sequentially with different scopes. Keep review read-only, require evidence, return fixes to one owner, and stop after two passes.
That workflow survives the next model release because it does not depend on a temporary benchmark lead. It depends on separation of duties, deterministic checks, and an explicit human decision at the end.