What comes on by default
The two entry points are not equivalent. A campaign upgraded because it uses Automatically Created Assets arrives with search term matching and text customization both enabled. A campaign upgraded because it uses campaign-level broad match arrives with search term matching only.
Search term matching is the query-side change: AI Max can serve against queries your keywords do not cover, on the model Google has been building toward since broad match absorbed close variants. Text customization is the creative-side change, and it is the larger of the two. It lets Google rewrite headline text rather than only add to it.
Where the notice leaves you
Google is emailing affected accounts, and the writeups so far describe eligible Search campaigns without defining eligibility. There is no published opt-out mechanism and no stated way to decline the upgrade in advance, which is the gap between now and September 1.
The risk in a migration like this is not the switch, it is the review that does not follow it. An account that has run automatically created assets since it was the default option is unlikely to have anyone reading its headline output today, and text customization changes what that output can be.
What to do about it
Audit which Search campaigns carry either setting
Campaign-level broad match and automatically created assets are both campaign settings rather than report dimensions, so this is a settings pass and not an export. Note which Search campaigns carry either one, then note which of those you would be unhappy to see rewritten. The second list is the one that needs attention on September 1.
Decide the headline question now
Text customization is the part of this that changes ad copy, and the decision it forces is whether your headlines are compliance-bound. Stores with claim language that anyone reviews, or with regulated product categories, should plan to switch automatic rewriting off after the upgrade rather than evaluate it later. Everyone else can leave it on and read the asset report through the first two weeks of September.