I’ve been super annoyed by the Siri dingus since upgrading to macOS 27. This morning I decided to find out if there was a way to get rid of it. Happily, someone pointed me to this post on Twitter (X) with the commands to remove it. I’ve run them, and they do appear to work. The post also contains the commands to re-enable it.
To disable it, run the following in Terminal:
sudo mkdir -p /Library/Preferences/FeatureFlags/Domain && \
sudo defaults write \
/Library/Preferences/FeatureFlags/Domain/WritingTools \
LightweightUI_macOS -dict Enabled -bool false
Once you have run these commands, you need to restart your Mac.