On March 7, Google made Gmail's Smart Compose feature available to all Android smartphone users, not just Pixel 3 owners.
Google's Smart Compose for Gmail, a feature that uses machine learning to offer you relevant text suggestions as you type emails, began rolling out to all Android devices yesterday, whether you're a Pixel 3 user or not, as spotted by Android Police
Previously, this technology was only available to desktop, G Suite, and – most recently – Pixel 3 users. Now, however, you'll have your own personal AI to help you write emails faster while away from the computer, even if you don't have a G Suite account.
Based on "your email writing patterns and some commonly used phrases", Smart Compose will offer text suggestion to speed up writing an email. If the prediction is useful, you can simply accept it or, if it's inaccurate, just continue typing.
The feature is enabled automatically but optional; it can be turned off in your Gmail settings. – AFP Relaxnews