Google is reportedly rolling out a new spam protection feature in its 'Messages' app as part of a server-side change that can be toggled on and off from the app's Settings menu by going into Settings > Advanced > Spam Protection.
Once the update goes through, users apparently get a message warning them that some of their data may be sent to Google for the feature to work as promised. According to the message, "To help protect against spam some data about your messages, but not any content, is set to Google".
As mentioned already, this is a server-side change, so you don't need to update your app to have it on your device. The change has just started rolling out, and should hit all users in the days ahead.
Screenshots Courtesy: Android Police