macOS 27 has a hidden "lightweight UI" for Siri AI when selecting text, here's how to enable it

[mactracker]

macOS 27 DB3/PB1 includes a hidden "lightweight UI" mode for Siri AI that comes up every time you select text.

When enabled, selecting text can display a floating contextual interface with actions, such as:

• The full Writing Tools suite, including Rewrite, Proofread, How does this sound?, and Edit with Siri
• Create Key Points, Summarize
• Add to Contacts, Message, Email
• Create Event
• Show in Maps
• Track Flight, Track Package

To enable, add a FeatureFlags override:

sudo mkdir -p /Library/Preferences/FeatureFlags/Domain && \
sudo defaults write /Library/Preferences/FeatureFlags/Domain/WritingTools.plist LightweightUI_macOS -dict Enabled -bool true

Then reboot your Mac. This is a private feature flag, and the UI is unfinished, with some actions failing, including Writing Tools.