The Review Bottleneck Is Real — and Getting Worse In April 2026, GitHub launched Stacked PRs into private preview — a native workflow for breaking large changes into chains of small, dependent pull requests. The timing wasn't accidental. As GitHub's Sameen Karim stated plainly: "The bottleneck is no longer writing code — it's reviewing it." This is a problem most engineering teams already know intuitively but rarely measure. The data, however, is stark. What the Numbers Say An analysis of over 50,000 pull requests across 200+ teams found that PRs over 1,000 lines have 70% lower defect detection rates than smaller ones. Extra-large PRs average 4.2 hours of review time but produce only 1.8 meaningful comments — fewer than small PRs reviewed in under an hour. The pattern is consistent: as PR size increases, reviewer fatigue sets in. Human working memory can track roughly 7±2 pieces of information simultaneously.…