They added it about 4-5 years ago, and really it just keeps getting better and better. I'm really in awe of the tech chops of the team that did this, especially around security. You'll often hear it referred to as crostini: https://chromeos.dev/en/linux

To be clear on what you're getting: It runs a (Linux) VM and you get root on (a container on) that VM. Not trying to rain on your parade (because it's really quite useful!) but it's limited in what it can do. (eg it can't change the host's wifi MAC address.)

Chromebooks have easy access to developer mode which gives you root access to the host OS though, so it's kinda moot.

Thanks for the detailed description. Might still consider it, or at least look for a cheaper Chromebook just to play around with and get a feel first.

At any rate, Chromebooks sound more capable than I previously gave them credit for, enough so that they will now be part of my evaluation next time I upgrade.

Between the Framework Laptop now supporting Chrome OS and some of the info in this thread, Chromebooks and Chrome OS no longer seem like just the cheap Google Docs appliances for schools that I originally thought they were, which is pretty cool.