GitHub ships stacked pull requests, and names agent throughput as the reason the review queue broke

Stacks are an ordered series of pull requests, each targeting the layer below it, reviewable in parallel and mergeable one, some or all at once, with existing branch protections still governing what reaches main. It installs as a CLI extension, gh extension install github/gh-stack, and GitHub says you can drive it "with a coding agent such as GitHub Copilot using the gh-stack skill." Merge queue support is "rolling out progressively over the coming weeks," so the piece that matters most for parallel agents is not there yet. Andy Merryman, CTO of TED, describes the resulting bottleneck: "AI has made TED's developers dramatically more productive, but that created a new bottleneck: PRs were growing large enough that reviewers were struggling."

Why it matters: Stacked pull requests give several dependent changes a way to land on one shared branch without contending, the forge-side equivalent of a local merge queue for parallel agents. A named customer stating on the record that agent output broke their review process is the clearest first-party evidence yet that the bottleneck has moved from writing code to landing it.