Since its launch last year, the embodiment of Google Assistant has been a somewhat robotic female voice. Starting now, you have your choice of that voice or a similarly robotic male voice. Google’s creative name for this one is “Voice II.”
The new voice is available in Assistant on Google Home and on phones. To set the male voice (probably US English only), open the settings on your phone Assistant or in the Google Home app. It’s under Preferences > Assistant Voice. You can have a listen to both voices below.
The settings carry over between the Home app and on-device Assistant, so you’ll always have a single Assistant voice on all your devices. The new voice should be available to everyone, but you might need to make sure your Google and Google Home apps are up to date.