Not seeing Assistant icon in search box

I have two phones. Both are Moto X4 running Android 9, with the same variant and security updates.

One shows the classic Google microphone icon in the search box. The other shows the Assistant icon.

All apps are up to date via the Play store. Both accounts have the Google Assistant enabled, and it displays when the home button is long pressed. The only difference I see is in the Google account to which each device is registered.

How can I get the Assistant icon on the top device?

Note I have also tried clearing data for the Google and Google Play Services apps, to no avail.