Google Docs' AI corrections are spreading to Gmail. Google is rolling out a feature in G Suite that will autocorrect "common" spelling errors while you write Gmail messages. It won't catch every mistake, but it should save you the embarrassment of leaving a glaring typo in a company-wide email. You'll also see grammar suggestions, too, helping you avoid common mistakes like confusing "affect" with "effect."
The feature is optional, and you can undo auto-corrected text if you move quickly.
It could be a while before you see this. The initial rollout focuses on G Suite's Rapid Release domains, who'll see the writing tool arrive within the next two weeks. It'll start rolling out to standard (Scheduled Release) G Suite users on September 12th. As for personal use? Google hasn't said yet -- it might be a while before they're available for everyday use.