Make the Second Reviewer Earn Its Place

A different model adds another chance to notice a defect; whether it adds useful coverage is something you have to test. Useful coverage means finding a real failure the existing review would have let through. Agreement, disagreement and comment volume are clues. None establishes that the change is wrong.

In his account of cross-model code review, paddo describes additional bugs found by reviewers from other model families. He also identifies limits in his comparison, including changes made between reviews and findings concentrated in a large pull request. Those observations justify a controlled trial. They do not tell you what your repository will gain.

Gunner Technology's position is that an extra reviewer should earn a defined job through evidence. Our post A Second Agent Is Not Independent Proof covers the authority boundary: the builder must not control its own verdict. Here the question is narrower. After you enforce that boundary, does another model catch enough additional trouble to justify running it?

Give each review route the same frozen code change, requirements and repository state. Frozen means the commit stays unchanged until the review reports have been saved. Otherwise a later reviewer may catch a bug introduced by an intervening fix, and you will mistakenly credit it with finding something the earlier reviewer missed.

Start with historical changes whose defects are understood, alongside changes checked for the failure types being evaluated. Preserve the code before each repair, but keep the later fix and incident explanation out of reviewer context. Include ordinary work from the queue you intend to review. A collection made entirely of dramatic incidents cannot show how much noise the reviewer will create on routine edits.

Compare the current route with the proposed addition under recorded limits for tools, context, time and spending. If you want to know whether model diversity helps, also try an extra pass with the current model under comparable limits. Otherwise you have tested more review against less review, without isolating the value of changing models. Save the reports separately before allowing either reviewer to see the other's conclusions.

An additional bug is a distinct, confirmed failure that the current route did not report on that same change. Group comments by the behavior they describe. Different wording or different line references can still point to the same defect. Count the failure once, and record which routes found it.

Require a finding to name the starting conditions, the action and the wrong result. Where possible, have a separate verification step reproduce that result against the frozen commit and check that a proposed repair removes it. A failing test needs an assertion tied to an accepted requirement. A test that merely repeats the reviewer's assumption cannot settle whether that assumption is correct.

Keep disputed findings unresolved until someone with responsibility for the behavior decides. Do not let the builder dismiss an objection just because it can produce a persuasive explanation. Do not let the new reviewer force a rewrite just because it sounds certain. Record confirmed defects, duplicates, unsupported reports and unresolved questions separately. An unresolved report is neither proof of a bug nor proof that the code is safe.

Include the review run, verification, repair, repeated checking and time spent resolving false alarms. A false alarm is a report that alleges a defect the evidence does not support. If an agent acts on it automatically, the cost can include a harmful code change followed by another repair. The model bill misses that work.

The Claude Code team describes evaluating reviewers against past incidents and checking noise on changes known to be clean. It also describes limiting review rounds after agents kept sending work back and forth. These are useful operating checks: measure what escaped, what was incorrectly flagged and whether the loop finishes.

Keep results separate for the work you might route differently. A reviewer that adds useful findings on permission changes may add only delay to copy edits. Record the consequence of each confirmed defect and the burden of investigating its reports. As Code Review Needs a Named Job argues, the review should answer a specific question. Its cost should attach to that job.

Keep it when the added protection meets acceptance criteria set before the trial, for a workload you can name. The person responsible for that workload should decide which missed defects are unacceptable and how much delay and investigation the route can afford. Do not choose those criteria after seeing which model looks best.

Start the candidate on a bounded queue in a repository you own, collecting reports without changing the existing release decision. This is shadow mode: the reviewer observes, while the established controls retain authority. Keep required human approval in place. If the evidence earns a blocking role, define which findings can stop work, how they get verified and when a disputed review goes to a person.

Set a limit on repair rounds and preserve the failure when the limit is reached. Recheck the route when its model, instructions or workload changes. The factory should collect reports, reproduce failures and enforce the stopping rule; people decide whether the protection earns its cost. Keep a useful reviewer for as long as the evidence supports its job. Retire an expensive source of comments.