Can you link to any actual evidence about this 10-20% productivity increase? And I don't mean anecdata like "I'm totally like 8200% more productive!1" that the AI bros love to spew.

From what I'm seeing at the Co I work for with ~1300 devs, productivity is more or less the same as it has always been. Projects aren't being done noticeably faster, there's no less bugs than before (if anything things are more unstable), the backlog remains endless. And we do all the crap that the AI hype tells us to do, we've got harnesses, complex agentic setups etc.