"A company like Microsoft" writes production code in literally every language.

The stakes are low and nobody cares if your little team writes code targeting a Brainfuck compiler. (Yes, this is a real thing; there's a Brainfuck compiler developed somewhere in the vast guts of Google. No, I don't have a link to share with you, sorry.)

> "A company like Microsoft" writes production code in literally every language.

Not in core parts of Windows they don't. It's C++, perhaps some C, and now Rust. It's a pretty big endorsement.

No. There's all sorts of hoary crap in the core parts of Windows - Pascal, C++, C, C# and various dialects thereof, JavaScript, Visual Basic, Prolog. This just off the top of my head.

It's not really an endorsement because the bar to getting into a Google or Microsoft or Facebook codebase is as low as it gets in this industry.

As someone who actually works at Microsoft, I can confidently say that a toy third-party language would have absolutely zero chance of getting approved for production code in any major shipping product. The first question that any manager will ask the developer pitching this is, "Where do I find the devs to maintain this codebase long term? And what happens if the language dies upstream?" - and you better have really good answers to those, or else a very convincing story explaining how the productivity boost is worth it.

Even Rust isn't all that easy. That it cleared the hurdle at all on so many teams already (and Windows especially!) is extremely impressive for a piece of tech so new.

> "Where do I find the devs to maintain this codebase long term? And what happens if the language dies upstream?"

This is the lowest of the low bars w.r.t. technology choice.

Compare, for example, to the vetting and QA the Linux kernel does.

Again, low or not, that is the bar that distinguishes fads from mature tech.

The question wasn't whether Rust is good or not, but rather whether it's entrenched enough to not be considered a mere fad anymore. Regardless of your opinion on the merits of Microsoft products or their development process, the point is that it's one of the largest software development companies, and - as enterprises tend to be - is more conservative in terms of technological stacks used for production code.