The Anthropic Claude Code team describes how it reviews code that is roughly 90% produced by Claude. Volume has exploded: in Anthropic's monorepo, daily changes rose from about 2,500 in May to more than 30,000 in September, and manual line-by-line review is no longer sustainable. From June to September, merged PRs on Claude Code more than doubled while the reverted share dropped by more than 40%.
Review serves two functions: catching defects and spreading knowledge of the code. For the first, the team replaces the question "did a human read it?" with "what check should catch what can go wrong?". The goal: most PRs merge with at most one human, with no increase in reverts or incidents, which act as a safeguard.
A change passes through several layers. Before the PR, Claude runs tests, build, and linter and shows the output, then a subagent reviews the diff in a fresh context. CLAUDE.md describes the project; REVIEW.md, written by the code owners, tells the reviewer what matters. On each PR, several agents hunt for bugs in parallel, others vote on each finding, and only the retained findings are published, sorted by severity. A separate security review and CI block the merge as long as an issue remains open. A classifier sets the risk level, and therefore the number of human approvers (zero, one, or two); some paths always require a person, and an agent's approval never counts as a human's. Merge queue, feature flags, internal use first, a latest channel ahead of stable, and fast rollback round out the setup.
The reviewer improves in a loop. PRs that caused incidents, confirmed by experts, form an eval replayed every day. Noise is measured by how authors react, since an agent fixes every nit and reruns a round. One PR went through more than fifty rounds in a single night; the team capped rounds at three, limited re-review to the new diff, and removed repeats, bringing the average down from 2.08 to 1.32 rounds.
Humans keep five decisions: whether to build it, risky code, architecture, reading the evidence, and accountability for the outcome. To understand the code, Claude is asked for an explainer of the relevant slice. The "you land it, you own it" norm relies on changes that are small and reversible. The article closes with a staged adoption list.