AdSense Backfill in Ad Manager: Before and After AdX

Many AdSense publishers who open Google Ad Manager do the obvious thing first: they connect AdSense, so their ad units keep earning while they learn the new platform. Google calls this option "Maximize revenue of unsold inventory with AdSense", and its MCM setup pages call it AdSense backfill. It is a sensible bridge. But when the time comes to switch on Ad Exchange through MCM, Google's setup steps ask you to turn it off first. This guide explains the three ways AdSense connects to Ad Manager, why that switch is required, and how to plan the handover so your pages are not left empty.

Three ways to connect AdSense to Ad Manager

Google describes three options for bringing AdSense demand into Ad Manager. You may have access to one or more of them.

Option 1: Network level. Use this when you want all or most of your ad units available to AdSense buyers. Go to Inventory > Network settings, select Maximize revenue of unsold inventory with AdSense next to "AdSense", and click Save. Google says activating AdSense for the network makes all ad units in the network available to compete with bids from AdSense buyers.

Option 2: Ad unit level. Use this when you only want some ad units available. Go to Inventory > Ad units, open an ad unit, select the same option next to "AdSense", and save. Google notes that ad unit settings for AdSense take precedence over network settings, so you can switch individual ad units off even with network-level AdSense on.

Option 3: Line items. If the AdSense line item type is enabled for your network, you can create AdSense line items (priority 12) and target specific inventory with extra targeting. If you do not see the type when adding a line item, Google says to talk to your Ad Manager administrator.

At network and ad unit level, Google says ad units automatically serve all relevant ad types and choose ad styles for you. Google also notes that AdSense does not serve on mobile apps. Whichever option you use, you do not need separate AdSense tags on your pages: Google says AdSense line items can be delivered through your Google Publisher Tags.

What "backfill" means here

"Backfill" describes AdSense's role: filling impressions that nothing else in your network has claimed, or that AdSense can pay more for.

Technically, AdSense in Ad Manager is eligible for dynamic allocation. That means it competes in real time against your other non-guaranteed demand, and against guaranteed line items through their temporary "opportunity cost" CPM. Google describes AdSense as offering fewer controls and more straightforward management than Ad Exchange, with demand from large third-party buyers including Google Ads. Our guide to dynamic allocation explains the auction in more detail.

Pricing rules can affect backfill too. Google lists AdSense backfill among the demand that pricing rules apply to, with the rules set in the Ad Manager network that makes the backfill request.

For many publishers new to Ad Manager, with no direct campaigns, AdSense backfill is in practice the main source of ads. That is why switching it off needs a plan.

Why MCM setup says to disable AdSense backfill before Ad Exchange

Google's page on MCM account setup options is explicit. In the setup where a child publisher uses its own Ad Exchange account under Manage Account, the steps for child networks say: if you use the AdSense backfill option, you must disable it before you can access the Ad Exchange feature.

The same steps add two more conditions that matter for timing:

• Don't enable Ad Exchange until approval is complete for all the sites you are monetizing. Google warns that if you enable Ad Exchange before site approval, ad serving will stop on sites that are unapproved.
• Update ads.txt after enabling Ad Exchange to include your new Ad Exchange code, which you can find under Admin > Global settings > Ad Exchange.

Google does not explain the reasoning on that page, so we will not guess at it. What matters is the order: approved sites first, then backfill off, then Ad Exchange on, then ads.txt.

To disable backfill, Google gives two routes:

• Network level: Inventory > Network settings, then uncheck Maximize revenue of unsold inventory with AdSense next to "AdSense".
• Ad unit level: Inventory > Ad units, open each ad unit, and uncheck the same box under "AdSense". Repeat for every ad unit that has it.

To find ad units that still have it on, Google suggests a filter in Inventory > Ad units: filter by Status (select Active, Inactive and Archived), then add a filter for AdSense enabled set to True. Once backfill is off at network or ad unit level, you can click Enable Ad Exchange to continue.

Planning the switch so pages are not left empty

The risk is a gap: backfill off, Ad Exchange not yet serving, and ad slots with nothing to show. The way to keep that gap small is to do the slow parts first.

Before the switch day:

1. Get every site approved. In Ad Manager, sites move through statuses such as Needs attention, Getting ready and Ready. Review usually takes a few days and can take up to 2 to 4 weeks. Google notes that for MCM, site review can start while the child is still completing its readiness steps, so do not wait.
2. Finish your MCM readiness steps, including identity and address verification, which Google requires of Manage Inventory children onboarded after April 3, 2024 (Google's identity verification page also lists Manage Account children).
3. Accept the Ad Exchange terms in the Ad Exchange setup screen under Multiple Customer Management.
4. List every ad unit with AdSense enabled, using the filter above, so nothing is missed.
5. Agree the plan with your MCM partner, including who does each step and when. Under Manage Account, the parent sets up pricing rules and other optimizations after you enable Ad Exchange.
6. Prepare the ads.txt change so it can go live straight away.

On the switch day:

1. Confirm all sites show as approved.
2. Turn off AdSense backfill at network level and on every listed ad unit.
3. Click Enable Ad Exchange.
4. Update ads.txt with your Ad Exchange code.
5. Load a few pages and check that slots fill. Do not click any ads to test them; use the Ad review center to check ads safely.

Pick a quiet day of the week for this, and avoid days when you expect a traffic spike.

Keeping your AdSense account in good standing

Turning off backfill does not mean you can forget about AdSense. Three reasons:

• Ad Manager depends on it. Google says you need a valid AdSense account to sign up for Ad Manager, and your Ad Manager account is permanently linked to it. You are not required to keep actively using AdSense, but the link remains.
• Breaches carry over. Google's Ad Manager Partner Guidelines say that if a partner breaches the terms of another Google product, such as AdSense, Google may suspend or terminate that partner's use of Ad Manager.
• History matters for MCM. The MCM Policies say child inventory must not have been previously disapproved by Google.

So keep the AdSense account tidy even after the switch. Resolve anything in its Policy center, keep your payment details current so any remaining balance can be paid, and do not reuse its code in ways that break placement or density rules. If you still have AdSense code on some pages during the transition, check those pages carefully so the two sets of ads do not crowd your content.

Payments change too. AdSense pays monthly, between the 21st and 26th, when your balance is over the threshold and there are no holds. Ad Manager has its own timeline: revenue for the previous month is posted by the 2nd, and payment is issued toward the end of the month. For a while you may receive payments from both. Our guide to the AdSense to AdX timeline shows how these steps fit together.

What to watch in reports the week after

The first week after the switch tells you whether the handover worked. Run a daily report broken down by ad unit and look at:

• Ad requests vs impressions. If requests are steady but impressions drop sharply on some ad units, those units may still have a setup problem.
• Ad units with no Ad Exchange activity. These are the ones to check first: tags, sizes and site approval.
• Unfilled impressions. Some unfilled impressions are normal. A sudden rise across the board suggests a floor or setup issue worth raising with your partner.
• Site statuses. Check Inventory > Sites for any site that has moved to Needs attention. Google lists ads.txt problems among the causes.
• Your Policy center. Make sure nothing new has appeared since the change.

Change one thing at a time, and give each change a few days before judging it. Daily numbers move around for many reasons, and a single day is rarely enough to tell signal from noise. Our guide comparing AdSense and Ad Manager is a useful refresher on what each platform controls.

Next step

AdSense backfill is a good bridge, and turning it off is the final step before AdX through MCM, not the first. Get your sites approved and your verification done, then make the switch in one planned session. If you want to see where you stand, check the requirements, and when your account and sites are ready, Get AdX access to request a review through our MCM partner network.