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The ads appear when you do search queries for news about a specific topic. For example, search for “Apple” and you get ads for Apple’s online store, search for “JetBlue” and you get ads for a variety of online ticket vendors. Like all Google products, the ads can be purchased through an AdWords account.
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Right now, the ads appear to be text-only, though Google alludes to some other formats in a blog post about the move. The company writes, “in recent months we've been experimenting with a variety of different formats, like overlay ads on embedded videos from partners like the AP.”