What Meta says
Meta describes an ad unit as a container that displays multiple ads, usually on the same page. With multi-advertiser ads on, your ad can appear in that unit next to personalized ads from other businesses that may or may not be related to yours, on Facebook Feed, Video on Facebook, Facebook Stories, Facebook Reels, Instagram Feed and Instagram Reels. (Meta Business Help Centre)
Why it's on by default
Meta's Marketing API documentation says new API-created ads created on or after August 19, 2024 are enrolled unless they explicitly opt out. Ads boosted from a Page or Instagram profile are opted in by default, and Meta warns the feature may be turned on automatically for existing ads that weren't explicitly opted out. In Ads Manager it appears as a ticked box under Ad setup at the ad level.
How to turn it off
Untick the Multi-advertiser ads box under Ad setup on each ad. To change many at once, select the ads in the Ads tab, click the arrow next to Edit, choose Multi-advertiser ads and untick Edit all selected ads. We untick it on every ad we build, for the reasons in turn off Meta's multi-advertiser ads.
The instant form version
Meta is gradually introducing multi-advertiser ads for instant forms. Your lead form can appear alongside forms from other businesses, and the page shown after someone submits can surface ads for other products and services. It may not be available in every account yet.
Common questions
What are multi-advertiser ads on Meta?
They let Meta show your ad inside an ad unit together with ads from other businesses on selected Facebook and Instagram placements. Meta says the ads are personalized to the viewer, may or may not be related, and your creative may be resized or cropped to fit.
How do I opt out of multi-advertiser ads?
At the ad level in Ads Manager, go to Ad setup and untick the box next to Multi-advertiser ads. For several ads, select them in the Ads tab, click the arrow next to Edit, choose Multi-advertiser ads and untick the box next to Edit all selected ads.
Are multi-advertiser ads turned on by default?
Effectively, yes. Meta's API documentation enrolls new API-created ads created on or after August 19, 2024 unless they opt out, boosted posts are opted in by default, and Meta says existing ads may be switched on automatically unless they were explicitly opted out.
Which placements can show multi-advertiser ads?
Meta lists Facebook Feed, Video on Facebook, Facebook Stories, Facebook Reels, Instagram Feed and Instagram Reels.
Can I opt out through the Marketing API?
Yes. Meta's Marketing API uses the contextual_multi_ads field on the ad creative, with enroll_status set to OPT_IN or OPT_OUT. Ads created on or after August 19, 2024 that don't specify it are opted in.