I have plenty of friends who are ex-Amazon engineers, and for all of their (valid) complaints about the place (management, incentive structure, culture, etc.), one thing no one has ever complained about was the efficiency and quality of Amazon’s engineering work. The stuff i heard about their internal build systems alone is straight up awe-inspiring, and that’s even compared to other tech giants (which is where i met most of the ex-Amazonians in the first place).

I think it's hard to generalize about anything as broad as engineering at companies at this scale. It's pretty clear they all have some really good engineering teams, especially on core functions. They also have some much weaker ones, and I've heard stories of flakiness from reliable people from all the big ones.

We're not talking to the same engineers. I hear about vast quantities of unmaintained code, still running, half-forgotten, across codebases in multiple languages, using ancient pre-AWS APIs

Sure, some teams might have their codebase in a really poor condition. Would be hard not to, given the size of the company.

But the core engineering stuff is high quality there. The build system that the whole company uses seems extremely well made. And I doubt that such a core thing can be done so well by a company with an overall poor engineering culture.

And the inverse seems to ring true as well. Even in large companies with overall poor engineering culture, you can find a few small pockets of teams that produce great small stuff. But they are fighting against the overall inefficiency of the company, while with Amazon, the opposite is happening, as poorly performing teams are being boosted by the core things (such as build systems) being done really well.

Interestingly enough, for each anecdote I head about the awe-inspiring internal build system, I hear a story from one of my ex-Amazon friends or coworkers about one time when they had to respond to a page about service for which they lost the source code.

Really? The parts of Amazon that matter, like retail and AWS, have very high engineering standards.

I have a friend who recently managed to spend 6 months without writing a single line of code, just getting shuffled from team to team (within Amazon retail), going to meetings, being reassigned, but not ever really being asked to do anything

That doesn't mean their engineering standards are low it means their efficiency is low.