thrust upon all users earlier this year. Smart Reply takes the context of the email message to which you are replying and what you have already typed to form a suggested completion to your sentence. These predictions appear in gray text as you type. To utilize the prediction just tap the tab key on your keyboard. And if you don't like the suggested text, just keep typing to ignore it. I use Gmail's Smart Reply function many times throughout the day as it does save me a few minutes crafting replies to emails.
If you haven't tried Smart Reply in Gmail (including Gmail accounts managed as part of G Suite for Education), you can enable it in your Gmail settings panel. To open your settings simply click on the gear icon that appears in the upper, right corner of your inbox (on a desktop or Chromebook). You will find Smart Reply about 2/3 of the way down the settings page.
Not everyone likes Smart Reply. If you're annoyed by the constant suggestions while you're typing an email, simply disable the feature from the same settings menu as is used to enable it.