Nope. It used to be a home baked solution that was totally unrelated to (and pre-dates) Zephyr. I believe that is the one that is still in the ChromiumOS EC repo, but for the last year or so, it's a Tock-based system.

Do you have a link for the Tock as the Chrome EC OS? My google-foo couldn't find anything.

"Starting roughly in July of 2021, Chromebooks switched from the original Google Chrome EC to an application based on the Zephyr Project RTOS."[0]

[0] https://chromium.googlesource.com/chromiumos/platform/ec/+/H...

EDIT: looks like there's something about Tock running on OpenTitan

https://opentitan.org/book/sw/device/index.html

Oh my apologies! I hadn't known about that intermediate version.

I don't know of a public announcement. Tock's license is acknowledged in Chromebook's licenses and those involved in Tock know simply because that team talks to us (a few of us interned on that team back when we were PhD students to help the effort at various stages as well).

It's not a secret, but it's also not something that seems to be high on anyone's todo list over there to announce.

It looks like Tock is also being used by Google for their security chips/dongles OpenTitan and OpenSK.

Correction, it's not the EC that runs Tock, but rather the GSC (the creatively named Google Security Chip). It used to run a system called Cr50 while recent versions run Ti50, which is Tock-based.