https://www.theverge.com/2019/1/3/18166628/android-messages-spam-protection-privacy-google

Google has confirmed that automatic spam protection within the default Android Messages app has begun rolling out to some users. The rollout was first spotted by Android Police. After displaying a notification to let the user know that the feature has been enabled, the app will begin analyzing messages that are sent to you in order to detect and proactively block spam messages. However, privacy concerns have been raised about the way the feature stores the associated phone numbers.

Automatic spam protection, which is opt-out by default, can be turned off from within the advanced settings menu. Google was unable to provide an exact timescale for the rollout of the new feature, but it said that it’s currently being released gradually in a few countries, and the company plans to release it more widely “in the coming months.”