Google launched its high-quality Home Max speaker with Google Assistant in October, and the last we heard (via a Best Buy leak), it was set to arrive on December 11th. That date was spot on, it turns out, as the Home Max has indeed gone on sale at both Best Buy and Verizon. It's also live on Google's own online store.
The Home Max speaker sports a pair of 4.5-inch high-excursion woofers and custom tweeters, putting it in the same class as serious audio products like the Sonos Play:5. We had a brief hands-on with it during the launch, under controlled conditions, and found it to be "extremely loud, well balanced and crystal clear, with well-defined bass."
Google Home Max, as mentioned, costs $399 and comes in charcoal and white with both Chromecast and the voice-controlled Google Assistant. That's $100 less than the Sonos Play:5, which doesn't have either of those two features. Sonos did say that Google Assistant was coming to the Sonos One in 2018 (it already supports Alexa), but there's no word on it coming to any other products.
Update: This post has been updated to clarify that the Home Max is also available directly from Google.