After half a year of development, spam protection in Android messages finally started rolling out earlier this month to some users. The feature is not yet available to anyone, which means that the change can be server-side and limited in the meantime. However, we can see a complete rollout once soon.
When the update comes to an Android phone, new messages will appear on the device showing the new spam protection. This new "spam protection" feature will also appear in the advanced section of the settings menu (Settings -> Advanced) so that users can manually enable or disable it.
A previously discovered part of Google's support help site that went live prematurely gave an explanation on how the new spam protection feature will work from a privacy perspective. Indicates that when this setting feature is enabled, some information about messages received on the device is automatically sent to Google. But the content of the message is not read; for example, the phone number or message body.
This spam protection feature is undefined, but possibly the data observes statistically to examine similarities between spam messages to detect them. If you send a spam report manually to Google, it still sends the phone numbers of both the sender and the recipient, including the message body. If you are so worried about privacy implications that may pose, and that Google has access to your information, you may not need this feature, probably using another app that can save you the hassle.