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

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.