The look of your News Feed isn't the only thing that's changing. Now Facebook is introducing a "small alpha test" that introduces targeted ads based on your activity outside of Facebook into your News Feed.
Previously, these kinds of ads only appeared on the right hand side of your Facebook profile. Facebook says:
"As part of this closed alpha test, we are working with a small number of demand side platforms (DSPs) including TellApart, MediaMath, and Nanigans. Over the coming weeks, we'll expand to make these ads available to additional DSPs and advertisers."
The social network also says that this will not change the overall number of ads you see in your News Feed.