Did your Google Ads performance tank in September 2026? Here's why.

The one-line version

Any Google Ads account running campaign-wide broad match or Automatically Created Assets (ACA) was eligible to be auto-migrated to AI Max for Search in late September. Google did it without opt-in. If your conversion rate fell off a cliff in the last two weeks of September while clicks and spend held steady, this is almost certainly why.

What actually happened

A notification appeared in affected accounts:

Search campaigns upgraded to AI Max for Search campaigns. Your campaigns using asset optimization are now AI Max for Search campaigns. Search term matching and text customization are enabled by default.

Nobody opted in. The trigger was having asset optimization enabled, which Google treated as consent to switch on two substantially larger features:

• Search term matching broadens the queries your ads appear for.
• Text customization rewrites your ad copy automatically.

The change does not appear in the account's change history. That log records user actions only. We pulled the full history for an affected account between 1 June and 9 October: nothing. As far as that log is concerned, the account was untouched for the entire month its performance collapsed.

What it did to one of our client accounts

A multi-city automotive services account, 13 campaigns, around $20k per month in spend. Comparing the first 27 days of September to 28 September through 8 October:

• Account overall: 19.2% to 14.0% conversion rate (-27%)
• City A, Service A: 19.9% to 4.2% (-79%)
• City A, Service B: 19.1% to 9.3% (-51%)
• City B, Service B: 16.3% to 9.5% (-42%)

The important detail: clicks did not fall. Impressions held (-1.6%), clicks held (-5.6%), spend held (+2.1%). Only conversions collapsed. Cost per click rose 8-11%. The same keywords converted a third worse than they had a week earlier.

Two campaigns broke on specific, adjacent dates. The daily data showed a step, not a slope:

• Mon 22 Sep: 14 clicks, 5.00 conversions, 23.6%
• Wed 24 Sep: 21 clicks, 5.33 conversions, 25.4%
• Sun 27 Sep: 27 clicks, 6.00 conversions, 22.2%
• Migration landed in this window
• Mon 28 Sep: 16 clicks, 2.00 conversions, 12.5%
• Tue 29 Sep: 21 clicks, 2.00 conversions, 9.5%
• Wed 30 Sep: 14 clicks, 0.00 conversions, 0.0%

How we proved it wasn't anything else

Before pointing the finger at Google, we eliminated every controllable cause:

• Website or forms? No. GA4 session conversion rate for paid traffic fell 38% while organic stayed flat on the same pages. A broken form can't tell where a visitor came from.
• Technical failure? No. Paid sessions arrived normally. No redirect fault, no tag failure.
• Anything we changed on our end? No. Nothing was changed in the account during that window. The account was static.
• Competitors? Opposite. Impression share went up in 9 of 11 campaigns and lost-impression-share-to-rank fell. We were winning more auctions, not losing them.
• Tracking? Our own database and Google's conversion counts agreed within 3 points. Offline conversion upload ran uninterrupted.
• Seasonality? All states fell in the same two weeks despite school holidays being staggered a fortnight apart between them.

Then the strongest evidence we had: we manage two other accounts in the same service verticals that were not migrated to AI Max. Both ran stable throughout the collapse period. Same manager, same industry, same country, same weeks. The migrated account's conversion rate halved. The two that escaped the migration were unaffected.

What we cannot definitively claim

The defensible claim is: every controllable cause was eliminated, the account was static, and the comparable accounts that escaped the migration were unaffected. Not: AI Max definitively caused this. But if you're seeing the same symptoms right now, you probably have the same cause.

How to fix it

Three steps, done in this order.

Step 1. Turn AI Max off (there is a glitch)

For some accounts the toggle appears to switch off on first try but doesn't actually save. The reliable sequence we found:

1. Click into the Search campaign

   Open the individual campaign from your campaigns list.

2. Refresh the page

   Hard refresh. This matters. Without it, the toggle has misbehaved for us.

3. Open Campaign Settings

   Scroll down and find AI Max for Search campaigns.

4. Toggle it off and confirm

   Click the toggle. A popup appears. Confirm Turn off.

5. Refresh the page again

   Open Campaign Settings a second time and verify the toggle is actually off. If it is still on, repeat the sequence.

6. Only then move to the next campaign

   Do it campaign-by-campaign. Account-wide bulk changes have been unreliable in our testing.

Step 2. Negative out the junk search terms

AI Max's search term matching spent your money on queries you would never choose yourself. Open Search terms for each affected campaign, filter by the last two weeks, and add every irrelevant query as a negative keyword at the campaign or ad group level. Expect to find a lot. The queries hiding in Google's Other search terms bucket (which hides roughly half your spend) are often where the worst matches sit. Scrutinise what you can see even more aggressively because of that.

Step 3. Add insurance against the next auto-migration

Google can do this again. Two things worth setting up now:

• URL exclusions at the account level for sites you never want traffic from.
• Review every account for Automatically Created Assets and asset optimization settings. If they are on and you do not actively use them, turn them off. These settings have been treated as implicit consent to broader changes.

Six things worth knowing before Google does this again

1. Google-initiated changes do not appear in your change history. An empty log proves only that you changed nothing.
2. Asset optimization was treated as consent to enable query matching and ad-copy rewriting. Check what features you have switched on that could serve as a migration trigger.
3. Keep one small unmigrated account open. It is the only real control available when Google changes something globally.
4. Measure with your own data. Google's conversion counts ran about 1.75x the actual leads in our database. Treat the Ads interface as a directional signal, not source of truth. Pull real revenue (or booked jobs, or qualified calls) from your own CRM and judge campaigns off that number.
5. The search terms report shows about half your spend. The rest is in the undisclosed Other search terms bucket. In one campaign, 60% of a day's clicks and 100% of its conversions came from queries we could not see.
6. Google's AI advisors inside the Ads UI were actively unhelpful during the diagnosis. Repeatedly misreporting campaign match types and sending the investigation down unrelated paths. Trust your own data.

Current status

AI Max switched off account-wide. Match types reverted. URL exclusions added as insurance against another automatic migration. Performance has started climbing back to pre-migration levels, with the clearest recoveries appearing on the campaigns where we have had the most time to negative-out the junk search terms AI Max had been spending on.

A question is still open with Google: a dated list of every automatic change applied to this account between 1 August and 8 October 2026. We will update this post when they send it. We are not holding our breath.