Google just launched its Artificial Intelligence engine and it is named "Bard". Surprisingly, Google decided to use a third level domain from its Google.com to launch this new service when it could have used its own .BRAND Top-Level Domain.
Bard can be tried at https://bard.google.com
What about Bard.google?
Well, first, at the date of this post's publication, it does not work and points to an error. Let's have a little imagination and read the front page of this product, it says; "Bard is an experiment and may give inaccurate or inappropriate responses. You can help make Bard better by leaving feedback."
Considering that it is an "experiment", let's hope that using a subdomain for such a big project is part of the experiment. I will definitely leave a feedback.