Excuse me for jumping in the middle of this (or the end, as the answer was provided already?)... Anyway:
I'm new here. Just joined the forum / community, and just installed my 16 zone gen 2 controller yesterday, replacing a 20 year old mechanical timer / controller (heavy, big metal case, 3 synchronous motors inside, etc.). Happily, all the zones came on when tested, and after some fiddling, I connected Google Assistant to my Rachio account, and Google Home now knows how to hand off the conversation to Rachio. I haven't gotten the request syntax down just yet, but at least I'm talking to Rachio, and I can control the sprinkler via the Android app, so it's just a matter of me spending a few minutes to learn how to do this properly.
The reason I jumped into this topic is that I wanted to note that when you establish multi-user capabilities with Google Home, as I have by adding my 3 other family members, it appears that you have to enable the Rachio<==>Google linkage for each and every connection. For ex: Google Home knows that I have connected my account to Rachio, and will let me "talk to Rachio", but my son, wife and daughter, while having personalized account access via our 3 Google Home's (and their phones), cannot yet "talk to Rachio", as I haven't yet connected their personal accounts to the Rachio account.
I'm not aware of a streamlined way to add ALL at once. This is just a heads up that if you have multiple users established with Google Home / Assistant, you'll need to link up each one with Rachio if you want to use voice control via Google Assistant with Rachio.