We knew it was coming in October, but Google officially announced today that starting October 17, Google Shopping results in the U.S. will start coming only from merchants who are Product Listing Ads advertisers.

“We will be ranking these results based on relevance, with bidding as an additional factor,” the company reiterates. “The ranking of natural search results on Google.com will not change.”

Google also announced the availability of product level bidding for product listing ads.

“You can now improve your Product Listing Ad performance by setting your cost per click bid at the item level,” says Sameer Samat, Vice President of Product Management, Google Shopping. “This functionality should help you meet your volume and profit targets at the product level.”

Advertisers/merchants can also create product targets using the product ID in their Merchant Center feed to manage bids at the product level.

Google is encouraging merchants to get set up in time for holiday advertising.

For more discussion on the positives and negatives of Google’s paid inclusion Google Shopping model, read this.