From generic style to personal style
Writing Tools introduced with macOS Tahoe could already rewrite, summarize, and correct. With macOS Golden Gate 27, Apple adds a relational dimension: the on-device model analyzes conversation history and learns how a user typically writes to each contact — more formal with a colleague, more direct with a friend — and generates drafts accordingly, as reported by 9to5Mac and MacObserver during keynote coverage.
Writing feedback as a separate feature
A distinct new addition is the ability to request feedback on your own writing: users can select a passage and receive critical suggestions, not just automatic corrections. This behavior is closer to an editorial tool than a spell-checker. Email draft generation happens directly in the text field, without opening a separate panel.
The privacy question
Contact-level personalization requires that the model access communication history. Apple provided no granular technical detail on whether processing happens on-device or via Private Cloud Compute, nor on which data is actually indexed. This is worth monitoring during the beta cycle, especially for those using Mail and Messages with corporate accounts.